Gay Male Only-Children: Evidence for Low Birth Weight and High Maternal Miscarriage Rates

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DOI: 10.1007/s10508-016-0829-9
Cite this publication
Abstract
Recent findings suggest that there may be a maternal immune response underpinning the etiology of sexual orientation of gay male only-children. This maternal immune response appears to be distinct from that which is purported to explain the classic fraternal birth order effect found in studies of male sexual orientation. We tested two predictions related to the hypothesized maternal immune response in mothers of gay male only-children: (1) elevated fetal loss among mothers who have had gay male only-children and (2) lower birth weight in gay male only-children. Mothers of at least one gay son (n = 54) and mothers of heterosexual son(s) (n = 72) self-reported their pregnancy histories, including the birth weights of newborns and number of fetal losses (e.g., miscarriages). Mothers of gay male only-children (n = 8) reported significantly greater fetal loss compared with mothers of males with four other sibship compositions (gay with no older brothers, gay with older brothers, heterosexual only-children, heterosexual with siblings) (n = 118). Also, firstborn gay male only-children (n = 4) had a significantly lower birth weight than firstborn children in the four other sibship compositions (n = 59). Duration of pregnancy was not significantly different among the groups of firstborn children in the birth weight analyses. Thus, this study found further support for a distinct pattern of maternal immune response implicated in the etiology of male sexual orientation. Mechanisms that may underlie this potential second type of maternal immune response are discussed.
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SPECIAL SECTION: THE PUZZLE OF SEXUAL ORIENTATION
Gay Male Only-Children: Evidence for Low Birth Weight and High
Maternal Miscarriage Rates
Malvina N. Skorska
1
Ray Blanchard
2
Doug P. VanderLaan
3,4
Kenneth J. Zucker
2
Anthony F. Bogaert
1,5
Received: 8 January 2016 / Revised: 24 May 2016 / Accepted: 2 August 2016 / Published online: 22 August 2016
Springer Science+Business Media New York 2016
Abstract Recent findings suggest that there may be a maternal
immune response underpinning the etiology of sexual orienta-
tion of gay male only-children. This maternal immune response
appears to be distinct from that which is purported to explain the
classic fraternal birth order effect found in studies of male sexual
orientation. We tested two predictions related to the hypothesized
maternal immune response in mothers of gay male only-children:
(1) elevated fetal loss among mothers who have had gay male
only-children and (2) lower birth weight in gay male only-chil-
dren. Mothers of at least one gay son (n=54) and mothers of
heterosexual son(s) (n=72) self-reported their pregnancy histo-
ries, including the birth weights of newborns and number of fetal
losses (e.g., miscarriages). Mothers of gay male only-children
(n=8) reported significantly greater fetal loss compared with
mothers of males with four other sibship compositions (gay with
no older brothers, gay with older brothers, heterosexual only-chil-
dren, heterosexual with siblings) (n=118). Also, firstborn gay
male only-children (n=4) had a significantly lower birth weight
than firstborn children in the four other sibship compositions (n=
59). Duration of pregnancy was not significantly different among
the groups of firstborn children in the birth weight analyses. Thus,
this study found further support for a distinct pattern of maternal
immune response implicated in the etiology of male sexual ori-
entation. Mechanisms that may underlie this potential second type
of maternal immune response are discussed.
Keywords Sexual orientation Birth weight Fetal loss
Miscarriage Birth order Maternal immune hypothesis
Introduction
The study of the biological origins of sexual orientation has
been ongoing for several decades now. Researchers investi-
gating sexual orientation have found evidence for the fol-
lowing biological correlates: genetics (e.g., Bailey, Dunne &
Martin, 2000; Bailey & Pillard, 1991; Hamer, Hu, Magnuson,
Hu, & Pattatucci, 1993; Mustanski et al., 2005; Sanders et al.,
2015), sex-dimorphic brain structures (e.g., Abe
´, Johansson,
Allze
´n, & Savic, 2014; LeVay, 1991; Witelson et al., 2008),
and hormones, particularly at the prenatal level (e.g., Bao &
Swaab, 2011; Ellis & Ames, 1987; Grimbos, Dawood, Burriss,
Zucker, & Puts, 2010;Hines,2011;Lalumie
`re, Blanchard, &
Zucker, 2000; Ngun, Ghahramani, Sanchez, Bocklandt, & Vilain,
2011). Whereas most of these findings apply to both men and
women, a different biological mechanism has been purported to
explain the fraternal birth order (FBO) effect that has been
found in studies of men’s sexual orientation.
In the FBO effect, the odds that men, but not women, will
be same-sex attracted as adults are increased with a greater
number of older brothers (for reviews, see Blanchard,
1997,2004,2008; Blanchard & VanderLaan, 2015; Bogaert
& Skorska, 2011; VanderLaan, Blanchard, Wood, & Zucker,
&Anthony F. Bogaert
tbogaert@brocku.ca
1
Department of Psychology, Brock University, 1812 Sir Isaac
Brock Way, St. Catharines, ON L2S 3A1, Canada
2
Department of Psychiatry, University of Toronto, 250 College
Street, Toronto, ON M5T 1R8, Canada
3
Department of Psychology, University of Toronto Mississauga,
3359 Mississauga Road N., Mississauga, ON L5L 1C6, Canada
4
Child, Youth and Family Division, Underserved Populations
Research Program, Centre for Addiction and Mental Health,
Toronto, ON, Canada
5
Department of Health Sciences, Brock University, 1812 Sir
Isaac Brock Way, St. Catharines, ON L2S 3A1, Canada
123
Arch Sex Behav (2017) 46:205–215
DOI 10.1007/s10508-016-0829-9
2014). A maternal immune mechanism is a hypothesized bio-
logical explanation for this effect. The hypothesis postulates
that with each successive male fetus the mother’s immune
system is repeatedly exposed (and thus potentially immu-
nized) to male-specific proteins associated with the Y-chro-
mosome, which a mother does not have. For a mother who has
been immunized, an increasing concentration of antibodies
develops after each male fetus and crosses the blood–brain
barrier to affect specific areas in the brain associated with the
development of sexual orientation, which would then influ-
ence the sexual orientation of later born sons (Blanchard &
Bogaert, 1996; Blanchard & Klassen, 1997). Recently, Blan-
chard (2012b) proposed a second maternal immune-based
explanation of the etiology of male sexual orientation that is
separate from the one related to the fraternal birth order effect.
Blanchard (2012b) found that in a sample of 44,981 hetero-
sexual and gay firstborn men, gay firstborns hadsignificantly
fewer younger siblings than heterosexual firstborns. As a possi-
ble explanation for this finding of fewer younger siblings in gay
firstborn men, Blanchard hypothesized that there might be a
maternal immune effect that increases the odds of a gay sexual ori-
entation in a subpopulation of firstborn sons and is associated with
a higher likelihood of fetalloss during other pregnancies. Thus,
this maternal immune effect would be at least partially distinct
from the classic FBO effect. This maternal immune effect should
also be more common among the subpopulation of mothers who
have had gay male only-children. The logic supporting the selec-
tion of this specific subpopulation of sons stems from studies tha t
suggest there are links between a maternal immune re sponse to a
fetus, a lower birth weight in a newborn, and secondary recurrent
miscarriage. Specifically, a maternal immune response to a fetus
can reduce the birth weight of a newborn and can prevent future
pregnancies from reaching full term, rendering the newborn an
only-child. Blanchard hypothesized that in addition to affecting
maternal fetal loss and the birth weight of the newborn, the indi-
vidual’s sexual orientation may be affected as well. To support
the logic behind this hypothesis, research literature supporting
the associations between a maternal immune response and fetal
loss andbetween a maternal immune response and birth weight,
areoutlinednext,andfollowedbysomerecentresearchon only-
children, sexual orientation, and birth weight.
A link between fetal loss and a maternal immune effect has
been posited in the scientific literature. There is evidence that
miscarriages in mothers partially reflect their immune response
to a male-specific protein—SMCY—important in male fetal
development (Nielson, 2011). SMCY has a relatively general-
ized role in the development of many structures of the body aside
from the brain during sexual differentiation. In sum, elevated
fetal loss may serve as a marker of a maternal immune response
(e.g., to SMCY or other male-specific proteins).
In addition to fetal loss, a second potential marker of a
maternal immune response is birth weight. An association
between low birth weight of offspring and a mother’s immune
system has also been advanced in the scientific literature. For
example, research in rodent models has demonstrated that male
pups had lower birth weight after maternal immunization to
male-specific antigens (Kahn & Baltimore, 2010). In human
studies, lower birth weight in both male and female offspring
was associated with a mother’s immune system activation during
pregnancy (Christensen et al., 2012; Kiefte-de Jong et al., 2013;
Kusanovic et al., 2007;Milns&Gardner,1989; Nielsen et al.,
2010; Silver et al., 2011) or when the mother and fetus show
antigen incompatibility (e.g., incompatible blood groups between
the mother and fetus) (Hoff, Peevy, Spinnato, Giattina, & Peterso n,
1993). These studies, however, have not investigated the associ-
ation among birth weight, sexual orientation, and sibship status.
There are two published studies examining birth weight in rela-
tion to sexual orientation and whether an individual was an only-
child or an oldest child (i.e., a firstborn with one or more younger
siblings).
Blanchard (2012a) demonstrated a significant interaction
between sexual orientation and sibship status (i.e., only-child
versus oldest child), such that the seven lesbian females and six
gay males who were only-children had a lower birth weight than
the 134 heterosexual females and 74 heterosexual males (and
there was no significant difference in birth weight between the
heterosexual and gay/lesbian oldest children). The mean differ-
ence in birth weight was 241.90 g (d=0.53). This pattern was
consistent with the hypothesis of a separate etiology for gay
male only-children, but both sexes were represented in these
analyses, and thus this study suggests that the separate maternal
immune etiology may not be specific to males.
VanderLaan et al. (2015) reported on a sample of 1722 male
and female children and adolescents, some of whom were clin-
ically referred for gender dysphoria andothers who were clinical
controls. Specifically, there were 1536 children (351 females,
1185 males) and 173 adolescents (72 females, 114 males). For
the children in their sample, the cross-gender behavior associ-
ated with gender dysphoria was treated as an indicator that sex-
ual attraction to the same natal sex was a probable adulthood
sexual orientation outcome among children (Green, 1987; Singh,
2012; Steensma, McGuire, Kreukels, Beekman, & Cohen-Ket-
tenis, 2013; Wallien & Cohen-Kettenis, 2008). For the adoles-
cents, sexual orientation was classified based on questionnaire
responses regarding sexual behavior and attraction. In this sam-
ple, the male only-children in the gender dysphoria group (n=
65) showed relatively lower birth weight compared with the
male only-children in the control group (n=167) (p=.07, d=
0.27 in males; p=.81, d=-0.06 in females). Thus, a similar
pattern emerged as in Blanchard (2012a), but the pattern in Van-
derLaan et al. (2015) was specific to males.
The goal of the current study was to replicate the birth weight
finding in males, given that not all findings for males have been
statistically significant. We focused only on natal male births
206 Arch Sex Behav (2017) 46:205–215
123
because our data set did not include information about lesbian
female births. Also, we conducted the first test of the fetal loss
prediction. Specifically, the current study employed a new data
set to explore whether gay male only-children have a lower birth
weightthan male childrenwith othersibship compositions. Also,
we examined whether mothers of gay male only-children have
experienced greater fetal loss (e.g., miscarriages) than mothers
of male children with other sibship compositions. We predicted
that (1) mothers of gay male only-children would have more fetal
loss than mothers of male children with other sibship composi-
tions and (2) gay male only-children would have a lower birth
weight than male children with other sibship compositions.
Method
Participants
A total of 159 individuals (12 men, 147 women) participated in a
larger study examining the association between a mother’s his-
tory of immunization to male-specific proteins (as inferred from
blood analysis) and her children’s sexual orientations. Partici-
pants were recruited via posters placed around an Ontario uni-
versity campus, advertisements placed on Kijiji, booths set up at
local Pride festivals, ads placed in local LGBT magazines and
radio stations, and ads placed in local newspapers. Ads were
targetedforthe specific samples requiredfor the larger study.
Specifically, ads asked that any interested‘‘mothers of son(s),’
‘mothers of gay son(s),’’‘‘mothers of straight/heterosexual son(s),’’
‘mothers of daughters only,’’and‘‘men only’’contact the laboratory
for more information about the study via e-mail or phone. Also,
six participants were mothers of males clinically referred to a spe-
cialty child and adolescent gender identity service for gender
dysphoria.
Of the 159 participants, 12 were men and 147 were women.
The women were further classified based on the sex and sexual
orientationof their offspring. Thus,59 were classifiedas mothers
of heterosexual son(s) only (i.e., could have daughters, but sons
were heterosexual only), 48 were classified as mothers of at least
one gay son (i.e., could have more than one gay son, could have
heterosexual sons as well, could have daughters), 11 were clas-
sified as mothers of daughters only(i.e.,nosons),sixwereclas-
sified as mothers of at least one natal male child clinically refer-
red for gender dysphoria (i.e., could have more than one natal
malechild who experiencedgender dysphoria, couldhave gay or
heterosexual sons, could have daughters), 13 were classified as
mothers of sons who had an unknown sexual orientation because
their sons were too young to know their sexual orientations (i.e.,
couldhave daughters aswell), threewere classifiedas mothersof
at least one transsexual individual, two were classified as moth-
ers of at least one bisexual son, andfivewereclassiedaswomen
who had no known pregnancies.
For the current study, a subsample of the recruited partici-
pantswas of interest.Specifically,wewereinterestedinthemain
groups from the larger study: mothers of at least one gay son and
mothersof heterosexual son(s)only. Thus, the mothersof hetero-
sexual son(s) only (n=59), mothers of at least one gay son (n=
48), mothers of at least one natal male child clinically referred for
gender dysphoria (n=6), and the mothers of sons who had an
unknown sexual orientation (n=13) were included in the cur-
rent study, for a total of 126 mothers. The mothers of at least one
natal male child clinically referred for gender dysphoria were re-
classified as mothers of at least one gay son becaus e most of these
gender dysphoric sons were likely to be gay men as adults (Green,
1987; Singh, 2012;Steensmaetal.,2013; Wallien & Cohen-
Kettenis, 2008). In total, then, 54 mothers had at least one gay
son. Similarly, the mothers of sonswho had an unknown sexual
orientation were re-classified as mothers of heterosexual son(s)
only, because 95–98 % of these children were likely to be hetero-
sexual as adults (Laumann, Gagnon, Michael, & Michaels, 1994;
LeVay, 2010). In total, then, 72 mothers were mothers of hetero-
sexual son(s) only. The majority of the 126 mothers were Cau-
casian (n=99 of the n=118 who completed the ethnicity ques-
tion; 78.6 %), and were attending or had completed a community
college diploma, university degree, or higher (n=94; 75 %).
Theiragesrangedfrom27to78years(M=51.30, SD =10.72).
Measures
Only the measures of interest to the current study are described
below.
1
Fetal Loss
Each mother was asked to report the outcome of her preg-
nancies. Outcomes were labeled by a mother as a miscarriage/
abortion, stillbirth, or live birth. For each mother, the number
of total miscarriages/abortions and stillbirths was tabulated
across all pregnancies to represent the fetal loss variable.
Thus, fetal loss represents the total number of fetuses/preg-
nancies that did not result in a live birth across all known
fetuses/pregnancies. In the rare instances of twins or multiple
fetuses for one pregnancy, each fetus was counted as one preg-
nancy and/or lost fetus. See‘‘Appendix’ for the form each
mother was asked to complete for each pregnancy.
Duration of Pregnancy
Each mother was asked to report the duration of a pregnancy
in weeks for pregnancies with all outcomes.
1
Please contact the corresponding author for a list of all measures.
Arch Sex Behav (2017) 46:205–215 207
123
Birth Weight
Each mother was asked to report the birth weight of each fetus in
pounds and ounces, grams, or else indicate that the birth weight
was unknown (e.g., if the fetus resulted in a miscarriage). Birth
weights reported in pounds and ounces were converted to grams.
Sex of Offspring
Each mother was asked to report the sex of each fetus using the
designation male, female, or unknown.
Sexual Orientation of Offspring
Each mother was asked to report the sexual orientation of each
live-born child using the labels heterosexual, gay, lesbian, bisex-
ual, transsexual,
2
or unknown. Mothers of natal male children
clinically referred for gender dysphoria did not answer a ques-
tion about the sexual orientation of their offspring. As indicated
above, most natal male children clinically referred for gender
dysphoria are likely to be homosexual as adults, with or without
continuing gender dysphoria.
Age of Mothers at Participation
Each mother was asked to report her date of birth. Age was cal-
culatedas the dateof examinationminus reporteddate of birth,in
years.
Procedure
A research assistant and phlebotomist met the participant at their
homeor on campus(whichever was mostconvenient). After pro-
viding consent, the participant completed a demographics and
pregnancy history questionnaire. Along with the measures of
reproductive history mentioned above, this questionnaire con-
tained questions related to demographic characteristics of the
participant (e.g., ethnicity, education). After completion of the
questionnaire, a sample of blood was drawn from the partici-
pant. Then, the participant was thanked, debriefed, and compen-
sated monetarily for their participation. This study was approved
by the necessary Research Ethics Boards.
Statistical Analyses
Fetal Loss Analyses
The 126 mothers were first re-classified into five groups based
on their pregnancy historie s: 8 mothers of gay male only-children,
23 mothers of gay males with no older brothers,
3
23 mothers of
gay males with older brothers, 11 mothers of heterosexual male
only-children, and 61 mothers of heterosexual males with sib-
lings. Analysis of variance (ANOVA) was used to test whether
there were any age differences among the five groups of mothers.
Helmert contrasts were used for planned comparisons to deter-
mine whether there were any differences among the five groups of
mothers (independent variable) in total number of fetuses lost
(dependent variable).
For five groups, Helmert contrasts compare Group 1 with the
mean of all later groups (i.e., 2, 3, 4, and 5); Group 2 with the
mean of all later groups (i.e., 3, 4, and 5); Group 3 with the mean
of all later groups (i.e., 4 and 5); and Group 4 with the mean of all
later groups (i.e., 5). The first three groups comprise the mothers
of gay males and the latter two groups comprise the mothers of
heterosexual males. Group 1 is designated as mothers of gay male
only-childrenbecause our predictions (basedon prior research and
theory) concern this group having the greatest number of fetal
losses. Group 2 is mothers of gay males with no older brothers
because their total reproductive output seems more similar to that
of Group 1 mothers compared with Group 3 mothers. Group 3 is
mothers of gay males with older brothers because that is the last
group of mothers within‘‘mothers of gay males.’’Group 4 is moth-
ers of heterosexual male only-children because this group seems
more similar to Group 1 in terms of total reproductive output than
Group 5. Group 5 is mothers of heterosexual males with siblings
because that is the remaining group. Omnibus ANOVA was not
performed because we had planned comparisons, and with plan-
nedcomparisons we canmove directly tothe comparisons(Tabach-
nick & Fidell, 2007,p.52).
A potential confound was that mothers would be expected to
have more fetal loss if they are likely to be pregnant more often
and thus have more children. Thus, as a second dependent vari-
able, a ratio of the number of lost fetuses to the number of live
births was computed.
4
Again, Helmert contrasts were used for
planned comparisons with the five groups of mothers as the inde-
pendent variable and the ratio variable as the dependent variable.
The same group ordering was utilized here as in the previous
analysis using Helmert contrasts.
Birth Weight Analyses
In the birth weight analyses, the units of analysis were selected
sons rather than the mothers. Because these sons did not actu-
ally participate in the study, they are referred to as subjects to
avoid confusion.
2
Although‘‘transsexual’’does not refer to sexualorientation,we included
thisdesignationundersexual orientationin the questionnaireto give moth-
ers another option if one or more of their children had a trans identity.
3
One of these mothers indicated that her son was gay/bisexual.
4
We decided to keep both analyses because the ratio variable is subject
to its own limitations (e.g., deviations from non-normality). Thus, we
believe a more complete picture can be gleaned from the data by
analyzing the fetal loss variable using both non-ratio and ratio variables.
208 Arch Sex Behav (2017) 46:205–215
123
In these birth weight analyses, we addressed a different
potential confound: Birth weight tends to increase over suc ceed-
ing pregnancies (Wilcox,Chang, & Johnson, 1996).To control
for this possible relation, we restricted the analysis to live-born
sons who were the result of their mother’s first known pregnancy
(n=63). In other words, we selected subjects who were identical
on maternal gravidity (number of pregnancies) and maternal
parity (number of deliveries) for their mother’s first pregnancy,
which is a stricter criterion than controlling for maternal parity
alone. Thus, a subset of the sample used to examine fetal loss
was used fo r the birth weigh t analyses because notall subjects
in the fetal loss data were firstborns.
For these birth weight analyses, it is easierto label the sons
according to their sibship composition rather than their
mothers’ reproductive histories, although there is a one-to-one
correspondence between the two frames of reference, as dis-
cussed below (see also Table 1). The sons were categorized as
follows: 4 gay male only-children, 7 gay males with no older
brothers, 14 heterosexual males with gay younger brothers, 10
heterosexual male only-children, and 28 heterosexual males
with siblings (other than gay younger brothers).
It is important to note the correspondence between the grou ps
of mothers studied in the analyses of fetal loss and the groups of
offspring studied in the analyses of birth weight (see Table 1).
This correspondence is immediately apparent in four of the five
instances (e.g., for the mothers of gay only-children, the off-
spring were gay only-children). The exception is the mothers of
gay males with older brothers, whose first-pregnancy offspring
were heterosexual males with gay younger brothers.
ANOVA was used to test whether there were any age dif-
ferences among the mothers of the five groups of subjects.
Helmert contrasts were used in planned comparisons to deter-
mine whether there were any differences among the five groups
of subjects (independent variable) in birth weight (dependent
variable). Groups were ordered the same way as their counter-
parts in the fetal loss analyses because there was no reason to
predict a different group ordering. As with the fetal loss analyses,
due to having planned comparisons, omnibus ANOVA was not
performed (Tabachnick & Fidell, 2007).
Results
Fetal Loss Analyses
The ANOVA with age at examination as the dependent vari-
able was marginally significant, F(4, 121) =2.43, p=.05.
Planned comparisons were not conducted because there were
no a priori expectations of age differences among the groups
of mothers used in the fetal loss analyses.
Of the 126 mothers in the sample, 40 reported a loss of 62
fetuses. All but two of these losses were reported as a miscar-
riage; in one of the remaining cases, the information was missing
and in the other case, the pregnancy resulted in a stillbirth.
Helmert contrasts revealed that a significant difference was
found between the mean of the Group 1 mothers compared
with the mean of all other groups (M
diff
=.84, SE =.36,
p=.02, 95 % CI 0.11, 1.56) (M
Group1
=1.25, SD
Group1
=1.39;
M
Group2
=0.43, SD
Group2
=0.79; M
Group3
=0.74, SD
Group3
=
1.71; M
Group4
=0.09, SD
Group4
=0.30; M
Group5
=0.39,
SD
Group5
=0.64). That is, the mothers of gay male only-children
had significantly greater numbers of fetal losses compared with
the mean of all other mothers (d=0.76; see Fig. 1). None of the
remaining Helmert contrasts was significant.
With ratio of lost fetuses to live births as the dependent
variable, Helmert contrasts revealed a significant difference
between the mean of the Group 1 mothers compared with
the mean of all other groups (M
diff
=1.09, SE =.18, p\
.001, 95 % CI 0.74, 1.44) (M
Group1
=1.25, SD
Group1
=1.39;
M
Group2
=0.14, SD
Group2
=0.26; M
Group3
=0.24, SD
Group3
=0.56;
M
Group4
=0.09, SD
Group4
=0.30; M
Group5
=0.17, SD
Group5
=
0.28). Thus, the mothers of gay male only-children had a
significantly greater mean ratio of the number of fetal losses
to number of live births compared with the mean of all other
mothers (d=1.55; see Fig. 2). Again, none of the remaining
Helmert contrasts was significant.
Given the typical non-normal distribution of ratio variables,
we also examined the ratio data using nonparametric statistics.
The most appropriate analysis is the Kruskal–Wallis test, which
is the nonparametric equivalent of an ANOVA (Field, 2013).
Themean ranks of theratio variable differedsignificantly among
the five groups of mothers, H=9.78, df =4, p=.04. There are
two possible ways to follow-up the Kruskal–Wallis test in SPSS
if the omnibus is significant (Field, 2013). We chose the‘step-
wise step-down’’option, which demonstrated that the mothers of
gay only-children were driving the significant omnibus H. Specif-
ically, the mothers of gay only-children were a separategroup
from the four other groups of mothers (mothers of gay males
with no older brothers, mothers of gay males with older brothers,
mothers of heterosexual male only-children, mothers of hetero-
sexual males with siblings) based on their mean ranks. The four
other groups of mothers, however, did not differ significantly
fromone another interms ofmean ranks (p=.58).Thus, themoth-
ers of gay only-children had a significantly greater mean rank of
the ratio of the number of fetal losses to number of live births com-
pared with the mean rank of all other mothers, convergent with the
results of the parametric test.
Birth Weight Analyses
TheANOVA with mother’sage atexamination as thedependent
variable was not significant, F(4, 58) =2.19, p=.08. Planned
comparisons were not conducted because there were no a priori
expectations of age differences among the groups of mothers
relevant for the birth weight analyses.
Arch Sex Behav (2017) 46:205–215 209
123
Planned comparisons using Helmert contrasts showed that
the predicted birth weight difference between the mean of
Group 1 subjects compared with the mean of all other groups
of subjects was significant (M
diff
=-615.73, SE =259.02,
p=.021, 95 % CI -1134.21, -97.25) (M
Group1
=2970.00,
SD
Group1
=623.48; M
Group2
=3713.71, SD
Group2
=488.28;
M
Group3
=3489.07, SD
Group3
=477.20; M
Group4
=3506.80,
SD
Group4
=411.93; M
Group5
=3633.32, SD
Group5
=517.41).
Thus, the mean birth weight of gay male only-children was
significantly lower than the mean birth weight of the first-preg-
nancy males in all other groups (Fig. 3). None of the remaining
Helmert contrasts was significant. In absolute terms, the differ-
ence in birth weight was approximately 600 g, representing a
large effect (d=1.21).
Additional Analyses Related to Birth Weight
We conducted a follow-up analysis to rule out another
explanation for the birth weight effect. Duration of pregnancy
did not differ among the same groups of subjects included in
the previous analyses, F(4, 58) =.38, p=.83. Thus, mean
duration of pregnancy of the first-pregnancy sons was virtually
identical for all groups of subjects (and close to the typical
40 weeks).
Discussion
In the current study, we found that mothers of gay male only-
children reported, on average, significantly greater mean fetal
loss compared with the mean of mothers of gay males with no
older brothers, mothers of gay males with older brothers, moth-
ers of heterosexual male only-children, and mothers of hetero-
sexual males with siblings, supporting Prediction 1. Notably, the
fetal loss effect was particularly evident for the ratio measure-
ment (fetal loss/live births), an arguably better measure than mean
absolutefetal loss, as the formeraccounts for overallnumber of
pregnancies. Further, we found that first-gestated gay male
Table 1 Correspondence between the groups included in the fetal loss analyses and the groups included in the birth weight analyses
Fetal loss analyses Birth weight analyses
Group name nPregnancy history Group name n
1. Mothers of gay male only-children 8 G 1. Gay male only-children 4
2. Mothers of gay males with no older brothers 23 e.g., GHH 2. Gay males with no older brothers 7
3. Mothers of gay males with older brothers 23 e.g., HHG 3. Heterosexual males with gay younger brothers 14
4. Mothers of heterosexual male only-children 11 H 4. Heterosexual male only-children 10
5. Mothers of heterosexual males with siblings 61 e.g., HH 5. Heterosexual males with siblings 28
Dependent variables
Number of fetuses lost by the mother
due to miscarriage, abortion, and stillbirth
Birth weight of the first-born male only
Ggay son, Hheterosexual son
Fig. 1 Mean (±SEM) number of
lost fetuses for each group of
mothers
210 Arch Sex Behav (2017) 46:205–215
123
only-children had, on average, a significantly lower mean
birth weight than the mean of first-gestated children in each
of the following sibship categories: gay males with no older
brothers, heterosexual males with gay younger brothers, hetero-
sexual male only-children, and heterosexual males with siblings
(other than gay younger brothers), supporting Prediction 2. We
have also ruled out a potential explanation of the duration of preg-
nancy for the birth weight finding. The former finding regarding
fetal loss is novel, whereas the latter finding regarding birth weight
is a partial replication and extension of the findings of Blanchard
(2012a) within males and VanderLaan et al. (2015).
The present study provided further support for Blanchard’s
(2012b) hypothesis of a separate etiology of male sexualorienta-
tion related to a mother’s immune response in gay only-children.
Specifically, two markers of a maternal immune response—high
fetal loss and low birth weight—were evident in gay male only-chil-
Fig. 2 Mean (±SEM) ratio of
lost fetuses to live births for each
group of mothers
Fig. 3 Mean (±SEM) birth
weight for each group of first-
pregnancy sons.‘Heterosexual
Males with Gay Younger
Brothers’are first-pregnancy
sons of mothers of gay males with
older brothers (cf. Figs. 1,2). The
category-label‘Heterosexual
Males with Siblings’’means
siblings that do not include a gay
younger brother
Arch Sex Behav (2017) 46:205–215 211
123
dren and in the mothers of these children. Indeed, the effects were
large (e.g., d=1.55 for fetal loss using the ratio measure, and
d=1.21 for birth weight), suggesting that a maternal immune
response may be a particularly powerful agent in the etiology of
gay male only-child individuals andinthefetallossoftheirmoth-
ers. In other words, low birth weight and high fetal loss may be
markers of a powerful form of a maternal immune response asso-
ciated with homosexuality in men, but one that is particularly
found in gay male only-children compared with male children of
other sibship compositions. This type of immune response may be
most detectable in gay male only-children because the absence of
additional siblings in gay male only-children is a sign that many of
their mothers may have been characterized by this powerful
immune response resulting in elevated fetal loss (and hence
no other children).
Regarding lower birth weight among gay male only-children,
the effect size found in the current study (d=1.21) was larger
compared with the effect size of d=0.53 found in Blanchard
(2012a)andd=0.27 found in VanderLaan et al. (2015). These
differences in effect size across studies may be due to the diver-
sity of the samples, the different and various sexual orientation
measures utilized in the studies, or the various sibship composi-
tion breakdowns in the studies. Further research with larger sam-
ple sizes and detailed sibship compositions will help to clarify
the effect size related to the birth weight of gay only-children.
We can only speculate about the specific maternal immune
mechanisms that underlie this potential second type of maternal
immune response. VanderLaan et al. (2015) postulated that moth-
ers who carry the HLA class II allele, HYrHLA, and a homozy-
gous 14 base pair in exon 8 of the HLA-Ggene would be more
likely to have a gay son. This hypothesis was proposed because
of previous literature indicating HYrHLA increased a mother’s
immune response to male-specific minor HY antigens; HYrHLA
was associated with low birth weight in firstborn sons (not first-
born daughters), and the homozygous base pair insertion in exon
8oftheHLA-Ggene was associated with greater miscarriages
after the birth of the first child (Christensen et al., 2012). The inves-
tigation of whether this specific genotype in mothers can explain the
putativesecond type of maternalimmune responsefound in the
current study, in Blanchard (2012a), and in VanderLaan et al.
(2015) will have to await future research.
There may also be different male-specific proteins asso-
ciated with the classic FBO maternal immune effect and this
second potential maternal immune effect associated with gay
only-children. As mentioned in the Introduction, SMCY is
reported to underlie fetal miscarriages (Nielson, 2011) and
thus this male-specific protein may play a role in the effects
associated with this second potential maternal immune
response in gay only-children. During sexual differentiation,
SMCY has a relatively generalized role in the development of
many structures of the body aside from the brain and thus
maternal anti-SMCY (e.g., antibodies to SMCY) likely has
dramatic effects on the fetus (i.e., miscarriage). If so, mothers
of gay only-children may be characterized by a powerful
immune response that includes reactions to a number of male-
specific proteins (including SMCY), which have particularly
powerful effects on additional male fetuses. In contrast, moth-
ers of gay men with older brothers may havehad a weaker but a
more specialized immune response to one or more male-speci-
fic proteins associated with brain development more directly
(e.g., PCDH11Y or NLGN4Y; for reviews, see Blanchard,
2008;Bogaert&Skorska,2011). Again, this speculation waits
further testing.
Limitations and Future Directions
This study cannot address the association between sibship com-
position, sexual orientation, and birth weight in women; as such,
Blanchard’s (2012a) finding that lesbian only-children had lower
birth weights than heterosexual female only-children—and Van-
derLaan et al.’s (2015) lack of such a finding—will require further
investigation. If the second type of maternal immune effect is
indeed replicated in women, the explanations posited in the cur-
rent study may not apply. For example, it may be the case that a
maternal immune response to a non-male-specific protein may
be occurring (Blanchard, 2012a); however, future research is
required to fully elucidate whether the effect occurs in women
and, if so, why. Also, studies utilizing a larger sample size will be
required to replicate and extend the current study. Blanchard’s
(2012a) suggestion of an online survey seems to be a straight-
forward methodological suggestion to managethe sample size
problem.Further,the currentstudyrelied on self-reportsof fetal
loss and birth weight. Although parent-reports of birth weight
seem to be very accurate (e.g., VanderLaan et al. reported r=
.97, p\.001for a subset of participants for whomboth hospital
records and parent-report birth weight were ava ilable), the accu-
racyof self-reports offetal lossmay bemuch lower.For example,
some women may experience a miscarriage without knowing
that one occurred. Hospital records and a longitudinal study
following mothers throughout their childbearing years may help
with determining whether self-reports are reliable indicators of
fetal loss; however, both options are less practical than the self-
reporting of fetal loss by mothers. Nevertheless, future research
incorporating other ways to measure fetal loss would be ben-
eficial.
Conclusion
We found that mothers of gay male only-children experienced
greater mean fetal loss compared with mothers of males with
other sibship compositions. Also, we found that first-gestated
gay male only-children had a lower mean birth weight than first-
gestated male children with other sibship compositions. In sum,
212 Arch Sex Behav (2017) 46:205–215
123
the current study provides additional support for the hypothesis
that a separate etiology of male sexual orientation related to a
mother’s immune response exists—one that is particularly pow-
erful and most detectable in gay male only-children.
Acknowledgments Thank you to J. Bramley, K. Fallis, I. Gabrie, J.
Gabrie, M. Hoffarth, L. Jamieson, K. Kilyk, K. Labanowicz, K. Lee, D.
Mahoney, S. Mazzuocco, S. Norgaard, K. Ross, K. Walczyk, C. Wang,
and N. Wickramasuriya for assistance with data collection. Thank you to
M. Ashton and D. Molnar for assistance with statistical analyses. Thank
you to C. M. McCormick for helpful comments on drafts of this paper. A
version of this paper was included in the Ph.D. dissertation for M. N. Sko-
rska. This research was supported by Natural Sciences and Engineering
Research Council of Canada grant to A. F. Bogaert and R. Blanchard [334-
737-007].
Compliance with ethical standards
Conflict of interest The authors declare no conflict of interest.
Human and animal rights and Informed consent All procedures
performed in studies involving human participants were in accordance
with the ethical standards of the institutional and/or national research
committee and with the 1964 Helsinki Declaration and its later amend-
ments or comparable ethical standards. Informed consent was obtained
from all individual participants included in the study.
Appendix: Questions mothers were asked to answer
regarding each pregnancy they experienced
Pregnancy number X
Your age at end of this pregnancy: _____
Father identifier (i.e., father of the fetus; first name, nickname, initials, number, etc.):_____
Medical problems during pregnancy—circle the answer: Yes No. If yes, please describe below.
Medical problems during delivery—circle the answer: Yes No. If yes, please describe below.
Any method of assisted reproduction (e.g., in vitro fertilization)—circle the answer: Yes No. If
yes, please describe below.
If this pregnancy resulted in one or more live births, does the child/children have (or had) any
medical/health issues—circle the answer: Yes No. If yes, please describe below:
Length of pregnancy (in weeks)_____
If a baby was delivered, method of delivery—circle the answer: C-section Natural.
Number of fetuses (babies carried) in this pregnancy: ____
Here is a table that asks about the outcome(s) of this pregnancy. Note that although most
pregnancies contain one fetus, we are listing up to four fetuses in the event of that you
carried more than one (e.g., twins) in this pregnancy.
Fetus/baby
number
Fetus
identifier
(first
name,
nickname,
initials,
number,
etc.)
Outcome—
miscarriage
or abortion
(MA),
stillbirth (S),
or live birth
(L)
Sex of
fetus—
male (M),
female (F),
or unknown
(U)
Writing
hand—
right (R),
left (L),
both (B),
or
unknown
(U)
Weight at
birth in
grams or
pounds
or
unknown
(U)
Sexual
orientationa
heterosexual (H),
gay (G), lesbian
(L), bisexual (B),
transsexual (T),
or unknown (U)
1
2
3
4
Did you intentionally try to have any more children after this pregnancy was finished?
___Yes ___No
aNote that mothers of natal male children clinically referred for gender dysphoria were not asked
to answer this question regarding the sexual orientation of each fetus.
Arch Sex Behav (2017) 46:205–215 213
123
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  • ... However, VanderLaan, Blanchard, Wood, Garzon, and Zucker (2015) only replicated the birth weight finding in male individuals referred for gender dysphoria and not in female individuals referred for gender dysphoria. Skorska, Blanchard, VanderLaan, Zucker, and Bogaert (2017) showed a lower birth weight in a sample of firstborn androphilic men who were onlychildren, and mothers of androphilic men who were only-children had more miscarriages than mothers of men with other sibship compositions. (Women were not investigated.) ...
    ... Regarding only-child status, we predicted that gynephilic women and androphilic men would be more likely to be onlychildren compared to androphilic women and gynephilic men, respectively (Blanchard, 2012a;Skorska et al., 2017;Vander-Laan et al., 2014, 2015. There was no only-child effect within men, but within women, gynephilic/biphilic women were more likely to be only-children than androphilic women, particularly when including biphilic women. ...
    ... The hypothesized explanation for the FBO effect in men is the MIH, which has recently received direct empirical support through the study conducted by Bogaert and colleagues (2018): controlling for total numbers of pregnancies, mothers of androphilic men with older brothers had the highest anti-NLGN4Y concentrations compared to mothers of androphilic men without older brothers, mothers of gynephilic men, and women with no sons. It is intriguing that only-child status was not related to sexual orientation in men given the results of previous studies (Blanchard, 2012a;Skorska et al., 2017;Van-derLaan et al., 2015). Interestingly, these studies also focused on the purported mechanism for the only-child findings by also investigating birth weight alongside only-child status. ...
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    The fraternal birth order (FBO) effect related to men’s sexual orientation refers to the finding that the number of older brothers that a man has increases his chance of being androphilic. The FBO effect has generally been well replicated in diverse samples; one instance of non-replication was by Francis (2008) using Waves I and III of the Add Health data. We attempted to replicate the FBO effect in the Add Health data taking into account family size and other limitations of Francis’ (2008) analyses. Also, we examined other sibling characteristics related to the FBO effect: sibling sex ratio and only-child status. We used two subsamples from Waves I (n = 20,745) and IV (n = 15,701) of the Add Health data, consisting of adolescents who were followed longitudinally from 1994 to 1995 until 2008. Wave I data were used to compute numbers of younger and older brothers and sisters from household roster information. Wave IV information about sexual orientation identity was used. Analyses were conducted within men and within women. We found modest support for the FBO effect in men, but not in women, using the older brother odds ratio, logistic regression analyses, and sibling sex ratio, which provided the strongest support for FBO. We found that gynephilic/biphilic women, but not androphilic/biphilic men, were more likely to be only-children compared to androphilic women and gynephilic men, respectively. We discuss limitations of the Add Health data and purported mechanisms for the FBO effect in men and the only-child effect in women.
  • ... In the same vein, a large proportion of participants in profile 1 did not report on one or more of the biomarkers (SI Appendix, Table S3); thus, many of these nonheterosexual men may have a biomarker but may not have reported it. Second, recent literature proposed mechanisms related to alternate (epi)genetic or maternal immune processes (59,(67)(68)(69). These processes and/or some alternate biodevelopmental processes yet to be proposed may apply to a portion of the profile 1 nonheterosexual men. ...
    ... These processes and/or some alternate biodevelopmental processes yet to be proposed may apply to a portion of the profile 1 nonheterosexual men. For example, profile 1 nonheterosexual men are more right-handed than the other groups and report a lower proportion of older brothers than do heterosexual men as well as compared with those in profiles 2 to 4 (SI Appendix, Subgroups of Nonheterosexual Men Differ from Heterosexual Men on Developmental Markers); perhaps mechanisms related to extreme right-handedness and only children/firstborns influence the development of nonheterosexual men in profile 1, as previously proposed (49,68). Third, psychosocial and cognitive developmental factors have been proposed and might apply. ...
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    Several biological mechanisms have been proposed to influence male sexual orientation, but the extent to which these mechanisms cooccur is unclear. Putative markers of biological processes are often used to evaluate the biological basis of male sexual orientation, including fraternal birth order, handedness, and fam-iliality of same-sex sexual orientation; these biomarkers are proxies for immunological, endocrine, and genetic mechanisms. Here, we used latent profile analysis (LPA) to assess whether these biomarkers cluster within the same individuals or are present in different subgroups of nonheterosexual men. LPA defined four profiles of men based on these biomarkers: 1) A subgroup who did not have these biomarkers, 2) fraternal birth order, 3) handedness, and 4) familiality. While the majority of both heterosexual and nonheter-osexual men were grouped in the profile that did not have any biomarker, the three profiles associated with a biomarker were composed primarily of nonheterosexual men. We then evaluated whether these subgroups differed on measures of gender non-conformity and personality that reliably show male sexual orientation differences. The subgroup without biomarkers was the most gender-conforming whereas the fraternal birth order subgroup was the most female-typical and agreeable, compared with the other profiles. Together, these findings suggest there are multiple distinct biodeve-lopmental pathways influencing same-sex sexual orientation in men.
  • ... [31][32][33] In a recent study, a distinct type of maternal immune response implicated in the etiology of male sexual orientation was investigated, with low birth weight and high fetal loss used as markers. 34 Like those of previous indirect measures of research used in the study of sexual orientation, low birth weight and high fetal loss are neither specific nor sensitive enough to be employed as markers. There are many contributing factors associated with low birth weight and its consequences. ...
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    Research into the neurobiological origins of same-sex attraction is inconclusive. A recent theory of homosexuality posited that maternal thyroid dysfunction during pregnancy is associated with an increased rate of homosexual orientation in offspring. Relevant studies from the prenatal thyroid model perspective were reviewed, the major findings of which are as follows: i) An increased prevalence of Hashimoto's disease in lesbian women suggests a maternal and even familial presence of the same autoimmune thyroid disease. Female-to-male transsexuals and lesbian women were also reported to have higher rates of polycystic ovary syndrome (PCOS). Over the last several years, reports suggesting a strong link between PCOS and thyroid autoimmunity have accumulated. ii) The increased risk of autism spectrum disorders (ASD) in the offspring of mothers with thyroid autoimmunity in pregnancy and the association between ASD and gender dysphoria indicate a link between maternal thyroid dysfunction and gender dysphoria/same-sex attraction in the off-spring. iii) The high risk of miscarriage and retarded fetal growth in pregnancies of mothers who give birth to homosexual off-spring can be explained by the impact of maternal thyroid dysfunction during pregnancy. This perspective review highlights relevant research findings and integrates them into the prenatal thyroid model of homosexuality. A better understanding of the mechanisms involved in the generation of same-sex orientation will contribute to the betterment of individual lives, as well as of society.
  • ... If so, the mothers of androphilic males should have fewer miscarriages than those of gynephilic males. Contradicting this possibility, however, is a study reporting that mothers of androphilic males had more miscarriages than mothers of gynephilic male (Skorska, Blanchard, VanderLaan, Zucker, & Bogaert, 2017). Nonetheless, this increase in fetal loss was specific to mothers of androphilic male only-children, whereas the same was not true for mothers of androphilic males with siblings. ...
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    Male androphilia (i.e., sexual attraction toward adult males) is influenced by biological factors, reliably occurs across diverse cultures, and has persisted over evolutionary time despite the fact that it reduces reproduction. One possible solution to this evolutionary paradox is the sexually antagonistic gene hypothesis (SAGH), which states that genes associated with male androphilia reduce reproduction when present in males but increase reproduction when present in their female relatives. The present study tested the SAGH among the Istmo Zapotec—a non-Euro-American culture in Oaxaca, Mexico, where transgender and cisgender androphilic males are known as muxe gunaa and muxe nguiiu, respectively. To test the SAGH, we compared offspring production by the biological relatives of muxe gunaa (n = 115), muxe nguiiu (n = 112), and gynephilic men (i.e., cisgender males who are sexually attracted to adult females; n = 171). The mothers and paternal aunts of muxe gunaa had higher offspring production than those of muxe nguiiu. Additionally, the relatives of muxe gunaa had more offspring than those of gynephilic men, whereas no such differences were found between the families of gynephilic men and muxe nguiiu. Elevated reproduction by the mothers and, particularly the aunts, of muxe gunaa is consistent with the SAGH. However, the absence of group differences between gynephilic men and muxe nguiiu, and the group differences between the two types of muxes are not predicted by the SAGH. This is the first study to demonstrate reproductive differences between kin of transgender and cisgender androphilic males within the same non-Euro-American culture.
  • ... However, other research suggests first-born homosexual males also have lower birthweights pointing to a distinct pattern of maternal immunity mechanisms different from that one associated with FBO (Skorska, Blanchard, VanderLaan, Zucker, & Bogaert, 2017). Xu et al. (2019) also found lower birthweight among nonheterosexual boys was unrelated to number of siblings. ...
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    This study tested whether previously reported associations between early life factors and later adolescent sexual orientation could be replicated in another prospective birth cohort, the UK Millennium Cohort Study (MCS). We used data on 9795 youth from the MCS. Emerging sexual orientation was assessed using measures of sexual attraction to males and females in separate items at 14 years. Factors including birthweight, breastfeeding, sibling composition, parental ages, maternal psychopathology, parent-child relationship, and contextual risks were separated into three developmental periods: prenatal (n = 5 factors), before 7 years (n = 6 factors), and after 7 years (n = 5 factors). We controlled for handedness as a putative marker of prenatal androgen exposure and the possibility of mischievous responding statistically. Girls with greater maternal psychological distress since age 7 and greater pubertal body mass index were more likely to be nonheterosexual but the effect sizes were very small. Among boys there were no significant associations between any early life conditions and later sexual orientation. However, focusing on effect sizes rather than significance levels, there were small associations between preterm birth and nonheterosexuality. The results offer further evidence that psychosocial influences in the development of adolescent sexual orientation are weak or non-existent.
  • ... Blanchard (2012) also proposed that mothers of firstborn homosexual sons were more likely to develop an immune response to a fetus, which may lower their birth weight (see also Bogaert et al., 2018). Again, results are inconsistent (Skorska, Blanchard, VanderLaan, Zucker, & Bogaert, 2017). It is also not clear why mothers of firstborn homosexual men without younger siblings would be more likely to develop an immune response. ...
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    This study tested the association between multiple prenatal and postnatal early life factors and adolescent sexual orientation in a longitudinal birth cohort. Factors included birth weight, gestational age, parental age at birth, number of older brothers and sisters, breastfeeding, maternal anxiety/depression, family socioeconomic position, parent–child relationships, parental absences, pubertal body mass index, and housing issues. We used data on 5,007 youth from the Avon Longitudinal Study of Parents and Children (ALSPAC). Sexual orientation was assessed using a 5-point scale of sexual attraction at 15.5 years. Early life factors were separated into three developmental periods: prenatal (n = 9), before 7 years (n = 5), and after 7 years (n = 5). We controlled for childhood gender nonconformity, handedness, and digit ratio as markers of prenatal androgen exposure. Gender nonconformity was strongly associated with later male and female nonheterosexuality, and higher right-hand digit ratio was associated with later male nonheterosexuality. Boys with low birth weight and shorter breastfeeding duration were more likely to have a later nonheterosexual orientation. Boys with parental absence before 7 years of age were more likely to be nonheterosexual, but this effect disappeared after entering all early life history factors. Parental absence since birth, low prenatal family socioeconomic position, and poorer parent–child relationship were associated with later nonheterosexuality among girls. The results are discussed in the context of a life history framework for understanding human sexual orientation development in males and females.
  • ... Despite finding evidence of the FBOE, we found no evi- dence for associations pertaining to birth weight, birth order, and gender expression in boys. As such, our findings did not align with the prior studies on birth order, birth weight and GD in birth-assigned male children ( VanderLaan et al., 2015), or those on gay men (Blanchard & Ellis, 2001;Skorska et al., 2017). These prior studies showed that groups of birth- assigned male children who experienced GD or were gay men had relatively lower birth weight compared to control groups if they were an only child or had one or more older brothers. ...
    Article
    Previous clinical research on children who experience gender dysphoria has demonstrated links between marked childhood gender variant behaviour and several variables thought to provide a window on biological processes affecting brain sexual differentiation during the pre-/perinatal period. These variables include handedness, birth order, and birth weight. The present study investigated, via parent-report, whether these factors were associated with inter-individual variation in childhood gender expression in a large community sample (n ¼ 2377, 51.4% boys). Consistent with previous studies, elevated gender variance was associated with non-right-handedness in boys and girls, and later fraternal birth order in boys. In contrast to prior clinical studies, there were no associations between gender expression and birth order in girls, and no interactions of birth weight and birth order in predicting gender variance in boys. Thus, handedness in both genders and late fraternal birth order in boys appear to apply widely as predictors of inter-individual variation in childhood gender expression, whereas the other factors examined here may only predict more marked levels of gender variance as examined in previous clinical research of children who experience gender dysphoria.
  • ... In research on heterosexual men, among the 20% who reported "some" homosexual feelings, a significantly greater number of older brothers was observed [73]. More recently, some studies have suggested that a maternal immune response may also cause low fetal weight, possibly influencing sexual orientation and gender-atypical behavior and identity among males [74]. ...
    Chapter
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    A number of studies have described lesbians in the United States as an underserved patient population. Among women in the United States, having a sexual orientation other than heterosexual is associated with increased rates of poor physical and mental health. This chapter will provide background to the ways that lesbians in the United States have been shown to be underserved in terms of health care and describe what clinicians can do to improve the quality of care provided to lesbian women, including detailed recommendations for gynecologic care in the outpatient setting.
  • ... In research on heterosexual men, among the 20% who reported "some" homosexual feelings, a significantly greater number of older brothers was observed [73]. More recently, some studies have suggested that a maternal immune response may also cause low fetal weight, possibly influencing sexual orientation and gender-atypical behavior and identity among males [74]. ...
    Article
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    Gynecologic Oncologists are sometimes consulted to care for patients who present with diverse gender identities or sexual orientations. Clinicians can create more helpful relationships with their patients if they understand the etiologies of these diverse expressions of sexual humanity. Multidisciplinary evidence reveals that a sexually dimorphic spectrum of somatic and neurologic anatomy, traits and abilities, including sexual orientation and gender identity, are conferred together during the first half of pregnancy due to genetics, epigenetics and the diversity of timing and function of sex chromosomes, sex-determining protein secretion, gonadal hormone secretion, receptor levels, adrenal function, maternally ingested dietary hormones, fetal health, and many other factors. Multiple layers of evidence confirm that sexual orientation and gender identity are as biological, innate and immutable as the other traits conferred during that critical time in gestation. Negative social responses to diverse orientations or gender identities have caused marginalization of these individuals with resultant alienation from medical care, reduced self-care and reduced access to medical care. The increased risks for many diseases, including gynecologic cancers are reviewed. Gynecologic Oncologists can potentially create more effective healthcare relationships with their patients if they have this information.
  • ... Instead the sexual orientation of gender-dysphoric boys was, as mentioned, classified as gay, based on research that indicates such boys are most likely to be gay men as adults (34,35). For a list of all pregnancy-related questions completed by the mother, see Skorska et al. (38). ...
    Article
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    We conducted a direct test of an immunological explanation of the finding that gay men have a greater number of older brothers than do heterosexual men. This explanation posits that some mothers develop antibodies against a Y-linked protein important in male brain development, and that this effect becomes increasingly likely with each male gestation, altering brain structures underlying sexual orientation in their later-born sons. Immune assays targeting two Y-linked proteins important in brain development-protocadherin 11 Y-linked (PCDH11Y) and neuroligin 4 Y-linked (NLGN4Y; isoforms 1 and 2)-were developed. Plasma from mothers of sons, about half of whom had a gay son, along with additional controls (women with no sons, men) was analyzed for male protein-specific antibodies. Results indicated women had significantly higher anti-NLGN4Y levels than men. In addition, after statistically controlling for number of pregnancies, mothers of gay sons, particularly those with older brothers, had significantly higher anti-NLGN4Y levels than did the control samples of women, including mothers of heterosexual sons. The results suggest an association between a maternal immune response to NLGN4Y and subsequent sexual orientation in male offspring.
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    Recent findings suggest that sexual orientation has an early neurodevelopmental basis. Handedness, a behavioral marker of early neurodevelopment, has been associated with sexual orientation in some studies but not in others. The authors conducted a meta-analysis of 20 studies that compared the rates of non-right-handedness in 6.987 homosexual (6,182 men and 805 women) and 16,423 heterosexual (14,808 men and 1,615 women) participants. Homosexual participants had 39% greater odds of being non-right-handed. The corresponding values for homosexual men (20 contrasts) and women (9 contrasts) were 34% and 91%, respectively. The results support the notion that sexual orientation in some men and women has an early neurodevelopmental basis, but the factors responsible for the handedness-sexual orientation association require elucidation. The authors discuss 3 possibilities: cerebral laterality and prenatal exposure to sex hormones, maternal immunological reactions to the fetus, and developmental instability.
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    Previous neuroimaging studies demonstrated sex and also sexual orientation related structural and functional differences in the human brain. Genetic information and effects of sex hormones are assumed to contribute to the male/female differentiation of the brain, and similar effects could play a role in processes influencing human's sexual orientation. However, questions about the origin and development of a person's sexual orientation remain unanswered, and research on sexual orientation related neurobiological characteristics is still very limited. To contribute to a better understanding of the neurobiology of sexual orientation, we used magnetic resonance imaging (MRI) in order to compare regional cortical thickness (Cth) and subcortical volumes of homosexual men (hoM), heterosexual men (heM) and heterosexual women (heW). hoM (and heW) had thinner cortices primarily in visual areas and smaller thalamus volumes than heM, in which hoM and heW did not differ. Our results support previous studies, which suggest cerebral differences between hoM and heM in regions, where sex differences have been reported, which are frequently proposed to underlie biological mechanisms. Thus, our results contribute to a better understanding of the neurobiology of sexual orientation.
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    Background: Findings from family and twin studies support a genetic contribution to the development of sexual orientation in men. However, previous studies have yielded conflicting evidence for linkage to chromosome Xq28. Method: We conducted a genome-wide linkage scan on 409 independent pairs of homosexual brothers (908 analyzed individuals in 384 families), by far the largest study of its kind to date. Results: We identified two regions of linkage: the pericentromeric region on chromosome 8 (maximum two-point LOD = 4.08, maximum multipoint LOD = 2.59), which overlaps with the second strongest region from a previous separate linkage scan of 155 brother pairs; and Xq28 (maximum two-point LOD = 2.99, maximum multipoint LOD = 2.76), which was also implicated in prior research. Conclusions: Results, especially in the context of past studies, support the existence of genes on pericentromeric chromosome 8 and chromosome Xq28 influencing development of male sexual orientation.
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    This study tested predictions regarding two hypothesized maternal immune responses influencing sexual orientation: one affecting homosexual males with high fraternal birth order and another affecting firstborn homosexual individuals whose mothers experience repeated miscarriage after the birth of the first child. Low birth weight was treated as a marker of possible exposure to a maternal immune response during gestation. Birth weight was examined relative to sibship characteristics in a clinical sample of youth (N = 1,722) classified as heterosexual or homosexual based on self-reported or probable sexual orientation. No female sexual orientation differences in birth weight were found. Homosexual, compared to heterosexual, males showed lower birth weight if they had one or more older brothers-and especially two or more older brothers-or if they were an only-child. These findings support the existence of two maternal immune responses influencing male sexual orientation and possibly also cross-gender behavior and identity. © 2014 Wiley Periodicals, Inc. Dev Psychobiol.
  • Article
    Homozygous carriage of a 14 base pair (bp) insertion in exon 8 of the HLA-G gene may be associated with low levels of soluble HLA-G and recurrent miscarriage (RM). We investigated the G14bp insertion(ins)/deletion(del) polymorphism in 339 women with unexplained RM and 125 control women. In all patients and patients with secondary RM after a firstborn boy, 19.2% and 23.9%, respectively, were G14bp ins/ins compared with 11.2% of controls (p<0.05 and p<0.01). Among secondary RM patients with a firstborn boy, G14bp del/del and no carriage of an HLA class II (HYrHLA) allele restricting immunity against male-specific minor HY antigens was found less often than in controls (p<0.05) whereas G14bp ins/ins and carriage of HYrHLA predisposed (p<0.08) to this clinical entity. The mean birth weight of firstborn boys born to G14bp ins positive secondary RM patients was significantly lower than expected (p<0.001) but only in carriers of HYrHLA alleles (p<0.01). In conclusion, homozygosity for G14bp ins predisposes to RM. The combination of G14 ins homozygosity and carriage of HYrHLA predisposes to secondary RM in women with a firstborn boy and negatively affects birth weight in these boys
  • Article
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    In adult male samples, homosexuality is associated with a preponderance of older brothers (i.e., the fraternal birth order effect). In several studies comparing gender dysphoric youth, who are likely to be homosexual in adulthood, to clinical or non-clinical control groups, the findings have been consistent with the fraternal birth order effect in males; however, less is known about unique sibship characteristics of gender dysphoric females. The current study investigated birth order and sibling sex ratio in a large sample of children and adolescents referred to the same Gender Identity Service (N = 768). Probands were classified as heterosexual males, homosexual males, or homosexual females based on clinical diagnostic information. Groups differed significantly in age and sibship size, and homosexual females were significantly more likely to be only children. Subsequent analyses controlled for age and for sibship size. Compared to heterosexual males, homosexual males had a significant preponderance of older brothers and homosexual females had a significant preponderance of older sisters. Similarly, the older sibling sex ratio of homosexual males showed a significant excess of brothers whereas that of homosexual females showed a significant excess of sisters. Like previous studies of gender dysphoric youth and adults, these findings were consistent with the fraternal birth order effect. In addition, the greater frequency of only children and elevated numbers of older sisters among the homosexual female group adds to a small literature on sibship characteristics of potential relevance to the development of gender identity and sexual orientation in females.
  • Objective: To examine the factors associated with the persistence of childhood gender dysphoria (GD), and to assess the feelings of GD, body image, and sexual orientation in adolescence. Method: The sample consisted of 127 adolescents (79 boys, 48 girls), who were referred for GD in childhood (<12 years of age) and followed up in adolescence. We examined childhood differences among persisters and desisters in demographics, psychological functioning, quality of peer relations and childhood GD, and adolescent reports of GD, body image, and sexual orientation. We examined contributions of childhood factors on the probability of persistence of GD into adolescence. Results: We found a link between the intensity of GD in childhood and persistence of GD, as well as a higher probability of persistence among natal girls. Psychological functioning and the quality of peer relations did not predict the persistence of childhood GD. Formerly nonsignificant (age at childhood assessment) and unstudied factors (a cognitive and/or affective cross-gender identification and a social role transition) were associated with the persistence of childhood GD, and varied among natal boys and girls. Conclusion: Intensity of early GD appears to be an important predictor of persistence of GD. Clinical recommendations for the support of children with GD may need to be developed independently for natal boys and for girls, as the presentation of boys and girls with GD is different, and different factors are predictive for the persistence of GD.