Deficiencies in reporting results of lesbians and gays after donor intrauterine insemination and assisted reproductive technology treatments: A review of the first emerging studies

Abstract

At a time when increasing numbers of lesbians and gays consider parenthood using reproductive assistance in infertility centers, the present review aims to summarize the results obtained so far by lesbians after intrauterine insemination (IUI) and in-vitro fertilization (IVF) using donor spermatozoa (D-IUI and D-IVF, respectively) and gays entering into gestational-surrogacy programs. Data show that gays display normal semen parameters and lesbians exhibit no specific causes of female infertility except perhaps for polycystic ovary syndrome (PCOS) and some PCOS-related factors. Pair-bonded lesbians entering into D-IUI programs, tend to have higher pregnancy and delivery percentages following spontaneous or induced ovulation than single or pair-bound heterosexual women. The only single study reporting success percentages of lesbians after D-IVF provides, however, puzzling results. In particular, pair-bonded lesbians have lower pregnancy and live-birth percentages than pair-bonded heterosexual women in fresh D-IVF cycles but percentages are similar in frozen/thawed D-IVF cycles. Like in lesbians after D-IUI, surrogate women recruited by pair-bonded gays/single men tend to have higher pregnancy percentages and lower miscarriage percentages than surrogate women recruited by heterosexual couples. Notably, all the reports reviewed in the present study are methodologically flawed because of sampling bias, small sample sizes and inadequate use of statistical methods to control for the effects of influential covariates including age, smoking habits, previous gynecological problems, hormonal stimulation type and protocol, and number of prior treatment types and pregnancies/deliveries. Clinicians, reproductive biologists and editors of fertility/infertility journals should make efforts to prevent these deficiencies in future data reporting.

Full text

R E V I E W Open Access
Deficiencies in reporting results of lesbians and
gays after donor intrauterine insemination and
assisted reproductive technology treatments: a
review of the first emerging studies
Juan J. Tarín
1*
, Miguel A. García-Pérez
2,3
and Antonio Cano
4,5
Abstract
At a time when increasing numbers of lesbians and gays consider parenthood using reproductive assistance in
infertility centers, the present review aims to summarize the results obtained so far by lesbians after intrauterine
insemination (IUI) and in-vitro fertilization (IVF) using donor spermatozoa (D-IUI and D-IVF, respectively) and gays
entering into gestational-surrogacy programs. Data show that gays display normal semen parameters and lesbians
exhibit no specific causes of female infertility except perhaps for polycystic ovary syndrome (PCOS) and some
PCOS-related factors. Pair-bonded lesbians entering into D-IUI programs, tend to have higher pregnancy and
delivery percentages following spontaneous or induced ovulation than single or pair-bound heterosexual women.
The only single study reporting success percentages of lesbians after D-IVF provides, however, puzzling results. In
particular, pair-bonded lesbians have lower pregnancy and live-birth percentages than pair-bonded heterosexual
women in fresh D-IVF cycles but percentages are similar in frozen/thawed D-IVF cycles. Like in lesbians after D-IUI,
surrogate women recruited by pair-bonded gays/single men tend to have higher pregnancy percentages and lower
miscarriage percentages than surrogate women recruited by heterosexual couples. Notably, all the reports reviewed
in the present study are methodologically flawed because of sampling bias, small sample sizes and inadequate use
of statistical methods to control for the effects of influential covariates including age, smoking habits, previous
gynecological problems, hormonal stimulation type and protocol, and number of prior treatment types and
pregnancies/deliveries. Clinicians, reproductive biologists and editors of fertility/infertility journals should make
efforts to prevent these deficiencies in future data reporting.
Keywords: Cause of infertility, Donor intrauterine insemination, In-vitro fertilization, Oocyte-donation cycles, Semen
parameters, Sexual orientation, Gestational surrogacy
Background
It has been reported that gays and lesbians reproduce
significantly less than heterosexual subjects. For instance
in one U.S. random-sample survey performed in 1994,
only 27 % of men who identified as homosexual said
they were fathers, compared with 60 % of other men.
Differences between groups were smaller in women but
the percentage was also lower in lesbians (67 % versus
72 % in other women) (for review, see [1]). Iemmola and
Camperio-Ciani [2] found in an Italian survey that non-
heterosexual men (bisexuals were also included in this
group) had significantly fewer children than heterosex-
ual men (an average of 0.12 versus 0.58 children/man).
Dissimilarities were even larger in a British study [3]
with an average of 0.002 children/man in exclusive
white homosexuals versus 0.36 children/man in white
heterosexuals.
Despite differences in number of children fathered,
there are no reasons to think that the potential for
reproduction of homosexuals is decreased when com-
pared with heterosexuals. Firstly, sexual preference is gov-
erned by the brain independently of plasma concentrations
* Correspondence: tarinjj@uv.es
1
Department of Functional Biology and Physical Anthropology, Faculty of
Biological Sciences, University of Valencia, Burjassot, Valencia 46100, Spain
Full list of author information is available at the end of the article
© 2015 Tarín et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain
Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article,
unless otherwise stated.
Tarín et al. Reproductive Biology and Endocrinology (2015) 13:52
DOI 10.1186/s12958-015-0053-9

of sex hormones as shown in the mouse model [4]. Like-
wise, plasmatic/salivary levels of sex hormones are not as-
sociated with sexual orientation in human beings (see
later). Secondly, there are more obvious reasons than de-
creased potential for reproduction to explain discrepancies
in number of children fathered between homosexuals and
heterosexuals. For instance, homosexuals do not engage in
sexual activities with individuals of the opposite sex as fre-
quently as heterosexuals.
Thanks to the social changes taking place in Western
society with respect to gay rights increasing numbers of
lesbians and gays seek reproductive assistance to achieve
parenthood in infertility centers. Consequently, a num-
ber of studies reporting success percentages of lesbians after
intrauterine insemination (IUI) and in-vitro fertilization
(IVF) using donor spermatozoa (D-IUI and D-IVF, respect-
ively) and gays entering into gestational-surrogacy pro-
grams are starting to emerge.
A priori, success percentages of lesbians and gays
should be similar or even higher than those exhibited by
heterosexuals attending infertility clinics. Actually, al-
though some studies suggest that some lesbians have
higher testosterone levels than heterosexual women, es-
pecially those that adopt a masculine role in their couple
relationship [5, 6], most studies find no significant differ-
ences between homosexual and heterosexual subjects in
adult plasmatic/salivary levels of sex hormones and go-
nadotropins, and secretion pattern of gonadotropins
([7–10] for reviews see [11–13]). In addition, pair-
bonded lesbians usually enter into D-IUI and/or D-IVF
programs to fulfill their wishes to get pregnant and have
their own offspring, not because they are infertile. In
contrast, most women from heterosexual couples attend
reproductive health clinics to undergo D-IUI and/or D-
IVF because their partner is an infertile man, human im-
mune virus (HIV)-positive, or carries another sexually
transmitted disease or a genetic disease. Of note, women
with an infertile partner may be as well subfertile, espe-
cially when their partner suffers from oligozoospermia
[14]. Moreover, lesbians may have a higher incidence of
polycystic ovary syndrome (PCOS) and some PCOS-
related factors including polycystic ovaries (see later),
circumstances that may increase further the success per-
centages after D-IUI and/or D-IVF. Indeed, women with
PCOS going through IUI [15–17] and women with poly-
cystic ovaries undergoing IVF and/or intracytoplasmic
sperm injection (ICSI) treatment [18–20] exhibit in-
creased pregnancy and live-birth/delivery percentages.
Likewise pair-bonded gays usually enter into gesta-
tional surrogacy programs to fulfill their desire to raise
children, create families and pass on their genes to off-
spring (for references, see [21]), not because they are in-
fertile. In contrast, pair-bonded heterosexual men use
these programs because their partner (a) has previously
experienced repeated implantation failure, unexplained
or failed treatment for recurrent pregnancy loss, or poor
obstetrical history; (b) has no uterus (congenital or post-
hysterectomy) or a severe Müllerian anomaly; (c) suffers
from a medical condition where pregnancy could pose a
significant health risk; or (d) takes medications that are
or could potentially be teratogenic [22]. Note that some
of these conditions in particular, recurrent pregnancy
loss [23–25] and repeated implantation failure (for re-
view, see [26]) not only may be associated with female
factors but also with male factors.
At a time when increasing numbers of lesbians and
gays consider parenthood using reproductive assistance
in infertility centers [22] the present review aims to
summarize the results obtained so far by lesbians after
D-IUI and D-IVF and gays entering into gestational-
surrogacy programs. This information may be helpful
not only to future intended homosexual parents seeking
reproductive assistance in infertility centers but also to
clinicians and reproductive biologists assisting this col-
lective. We are aware that human sexual behavior is
highly complex and variable and sexuality is much
more complex and individual than a simpler bipolar
(heterosexual versus homosexual) classification [27].
However, for the sake of simplicity and pragmatism, we
use the traditional bipolar classification.
Methods
A literature review based on publications up to February
2015 identified by PubMed database searches using the
following key words: lesbians, gays, homosexuals, hetero-
sexuals, sexual orientation, fertility, infertility, gestational
surrogacy, reproductive fitness, intrauterine insemination,
in vitro fertilization, testosterone, estradiol, steroids, hor-
mone profiles, gonadotropins, oligozoospermia, terato-
zoospermia, asthenozoospermia, normozoospermia. In
addition, a hand search was done to explore the references
cited in the primary articles. This literature search evi-
denced 4 and 2 articles reporting success percentages of
lesbians and gays, respectively, after D-IUI and assisted re-
productive technology treatments (see Tables 1 and 2). All
these articles were analyzed without applying inclusion or
exclusion criteria.
For the sake of uniformity, data from 2 × 2 and 3 × 2
contingency tables were re-analyzed using Pearson's
chi-square test. Fisher’s exact test was applied in the
analysis of 2 × 2 contingency tables if the expected
values in any of the cells were less than 5. Data re-
analysis was performed using the IBM SPSS Statistics,
Version 22 (© Copyright IBM corporation et al. 1989,
2013). P values from tests comparing continuous vari-
ables were kept in their original form. Significance was
defined as P ≤0.05.
Tarín et al. Reproductive Biology and Endocrinology (2015) 13:52 Page 2 of 7

Causes of infertility in lesbians
Despite a higher prevalence of Chlamydia infection [28,
29], the incidence of tubal-factor infertility in lesbians is
similar to that found in heterosexual women [29–31].
However, two articles [10, 31] have reported that, com-
pared with heterosexual women, lesbians may exhibit
higher prevalence of PCOS and some PCOS-related fac-
tors including polycystic ovaries, hirsutism, obesity, and
Table 1 Success percentages of lesbians after D-IUI,fresh D-IVF and frozen/thawed D-IVF
Treatment Outcome Ovarian
stimulation
Lesbians Pair-bonded
lesbians
Pair-bonded
heterosexual
women
Single women Single
heterosexual
women
Pvalue Reference
D-IUI Pregnancy per cycle None 22.2 (10/45)
a
8.8 (19/217) 0.016
b
Ferrara
et al. [30]
hMG 20.8 (5/24) 10.4 (14/134) 0.172
b
Ferrara
et al. [30]
CC 7.2 (5/69) 5.4 (10/185) 0.560
b
Ferrara
et al. [30]
None, CC
or hMG
13.5
(26/192)
9.6 (83/864) 0.105
c
Ferrara
et al. [38]
None, CC, FSH
or CC+ FSH
20.5 (90/438) 14.8 (44/298) 0.046
c
Nordqvist
et al. [29]
Ongoing pregnancy
per woman after a
mean number of
3 cycles
None, CC or
gonadotropins
≈60 %
(≈72/120)
d
≈55 %
(≈72/131)
d
0.203
c
De Sutter
et al. [33]
Pregnancy per
woman after a mean
number of ≈3 cycles
e
None, CC, FSH
or CC+ FSH
61.6 (90/146) 44.0 (44/100) 0.006
c
Nordqvist
et al. [29]
Live-birth per cycle None, CC, FSH
or CC+ FSH
16.0 (70/438) 12.8 (38/298) 0.224
c
Nordqvist
et al. [29]
Live-birth per woman
after a mean number
of ≈3 cycles
e
None, CC, FSH
or CC+ FSH
48.0 (70/146) 38.0 (38/100) 0.123
c
Nordqvist
et al. [29]
Fresh
D-IVF
Pregnancy per cycle Not specified 34.6 (44/127) 45.2 (57/126) 0.085
c
Nordqvist
et al. [29]
Pregnancy per
woman after a mean
number of ≈1.5
cycles
f
Not specified 47.8 (44/92) 68.7 (57/83) 0.005
c
Nordqvist
et al. [29]
Live-birth per cycle Not specified 27.6 (35/127) 33.3 (42/126) 0.318
c
Nordqvist
et al. [29]
Live-birth per woman
after a mean number
of ≈1.5 cycles
f
Not specified 38.0 (35/92) 50.6 (42/83) 0.095
c
Nordqvist
et al. [29]
Frozen/
thawed
D-IVF
Pregnancy per cycle Not specified 31.6 (31/98) 31.7 (33/104) 0.988
c
Nordqvist
et al. [29]
Pregnancy per
woman after a mean
number of ≈2 cycles
g
Not specified 63.3 (31/49) 64.7 (33/51) 0.881
c
Nordqvist
et al. [29]
Live-birth per cycle Not specified 24.5 (24/98) 23.1 (24/104) 0.814
c
Nordqvist
et al. [29]
Live-birth per woman
after a mean number
of ≈2 cycles
g
Not specified 49.0 (24/49) 47.1 (24/51) 0.848
c
Nordqvist
et al. [29]
a
Counts used to calculate percentages are shown in parentheses
b
2 × 2 contingency Fisher’s exact test
c
2 × 2 conting ency Pearson’s chi-square test
d
Data were represented in a graphical format. Thus, we do not know the exact number of women with an ongoing pregnancy
e
3.00 (438/146) and 2.98 (298/100) D-IUI cycles per woman in the lesbian and heterosexual group, respectively
f
1.38 (127/92) and 1.52 (126/83) D-IVF cycles per woman in the lesbian and heterosexual group, respectively
g
2.00 (98/49) and 2.04 (104/51) D-IVF cycles per woman in the lesbian and heterosexual group, respectively
Tarín et al. Reproductive Biology and Endocrinology (2015) 13:52 Page 3 of 7

higher testosterone and androstenedione levels. A third
study [32] has shown that although lesbians with PCOS
display higher body mass index than heterosexual women
with PCOS, they have similar hyperandrogenism-related
clinical or biochemical characteristics. Likewise, other
studies [29, 33] have found no significant differences in in-
cidence of PCOS and polycystic ovaries between lesbians
and heterosexual women.
Seminal parameters in gays
There is a total absence of current studies reporting
seminal parameters in gays. Just a limited number of ar-
ticles published in the 60’sand70’s decades dealt with
this topic. Most of them evidenced no significant differ-
ences in semen parameters between homosexual and
heterosexual men [34–36]. Only one article by Kolodny
et al. [37] reported the presence of significant differ-
ences in sperm counts among groups of homosexuals
established according to the Kinsey’s heterosexual-
homosexual rating scale. In particular, azoospermia and
oligozoospermia were concentrated in men with ratings
5 or 6 on the Kinsey’s scale, i.e., men almost exclusively
or exclusively homosexuals, respectively. These data,
however, should be taken with caution because Kolodny
et al. [37] did not control for several covariates that
may influence seminal parameters such as health status,
use of psychotropic drugs, and degree of physical exer-
cise and sexual activity. In addition, the Kinsey’srating
procedure did not discriminate between overt behavior
only or the subjects’general sexual responsiveness in-
cluding attraction and fantasies.
Success percentages of lesbians after D-IUI and D-IVF
D-IUI
Table 1 shows that lesbians tend to have higher success
percentages than heterosexual women after D-IUI. Fer-
rara et al. [30] reported a significantly higher pregnancy
percentage per D-IUI cycle in pair-bonded lesbians fol-
lowing spontaneous ovulation than in single women
(22.2 %, versus 8.8 %). After ovarian stimulation with go-
nadotropins (20.8 % versus 10.4 %) or clomiphene citrate
(7.2 % versus 5.4 %), pair-bonded lesbians still showed
higher pregnancy percentage per cycle although differ-
ences were not significant. Differences between groups
may be explained by the younger age of pair-bonded les-
bians (mean age: 34.5 years; range: 26–44 years) com-
pared with single women (mean age: 38.5; range: 29–47
years; P ≤0.005). Furthermore, some single women may
have had a previous infertile relationship with a hetero-
sexual partner and, therefore, at least some of them may
have been subfertile. We should note, however, that
pair-bonded lesbians under 35 years of age exhibited
higher, although not statistically significant, pregnancy
percentage per D-IUI cycle than single women from the
same age group (23.9 %, 16/67 versus 11.5 %, 7/61; Pear-
son’s chi-square test: P ≤0.068). Likewise, in women 30–
35 years old, miscarriage percentage per pregnant
woman was significantly lower in pair-bonded lesbians
(10.0 %, 1/10 versus 66.7 %, 4/6 in single women; Fish-
er’s exact test: P ≤0.036). Noteworthy, differences be-
tween groups may have been even higher if we take into
account that some lesbians may have been included in-
correctly in the group of single women. A later study
from the same group [38] reported also a higher, al-
though not significant, pregnancy percentage per D-IUI
cycle in lesbians compared with single heterosexual
women (13.5 % versus 9.6 %). Of note, Ferrara et al. [38]
on this occasion did not specify whether or not lesbians
were pair-bonded and did not compare the effect of
ovarian stimulation on pregnancy percentage between
lesbians and heterosexual women.
Another study by De Sutter et al. [33] evidenced a
non-significant higher ongoing pregnancy percentage
per woman in pair-bonded lesbians than in pair-bonded
Table 2 Success percentages of gays entering into gestational-surrogacy programs
Treatment Outcome Pair-bonded
gays/single men
Heterosexual
couples
“Failed to
carry”
heterosexual
couples
a
“Cannot carry
pregnancy”
hererosexual
couples
b
P
value
Reference
Gestational-
surrogacy
program
Delivery per surrogate woman after a
maximum of either two fresh cycles or
one fresh and one frozen transfer
cycle
55.6 (25/45)
c
48.9 (23/47) 0.525
d
Grover et al. [21]
Pregnancy per cycle
f
59.7 (37/62) 50.0 (66/132) 54.0 (75/139) 0.447
e
Dar et al. [22]
Miscarriage per pregnant surrogate
woman
10.8 (4/37) 25.8 (17/66) 20.0 % (15/75) 0.193
e
Dar et al. [22]
a
96 pati ents suffering from recurrent implantation failure (n = 57), recurrent pregnancy loss (n = 30) and previous poor pregnancy outcome (n = 9)
b
108 patients suffering from uterine malformations/Asherman’s syndrome (n = 34), Müllerian agenesis (Mayer–Rokitansky–Kuster–Hauser syndrome; n = 33) and
maternal medical conditions precluding pregnancy (n = 41)
c
Counts used to calculate percentages are shown in parentheses
d
2 × 2 contingency Pearson’s chi-square test
e
3 × 2 contingency Pearson’s chi-square test
f
A cycle was defined as one stimulation cycle with fresh transfer and any subsequent frozen embryo transfer from the same cycle
Tarín et al. Reproductive Biology and Endocrinology (2015) 13:52 Page 4 of 7

heterosexual women (≈60 % versus ≈55 %) after a mean
number of 3 D-IUI cycles. Notwithstanding, this study
did not either control for women’s age (mean age:
30.6 years in lesbians versus 31.9 years in heterosexuals)
and hormonal stimulation [none, clomiphene citrate
(CC) or gonadotropins]. We should bear in mind that,
in contrast to Pearson’s chi-square test, binary logistic
regression models allow you to control for categorical,
interval or continuous covariates.
More recently, Nordqvist et al. [29] have reported a
significantly higher pregnancy percentage per D-IUI
cycle (20.5 % versus 14.8 %) and per woman after a
mean number of ≈3 D-IUI cycles (61.6 % versus 44.0 %)
in pair-bonded lesbians compared with pair-bonded het-
erosexual women. Live-birth percentage per D-IUI cycle
(16.0 % versus 12.8 %) and per woman after a mean
number of ≈3 D-IUI cycles (48.0 % versus 38.0 %) were
also higher in the homosexual group, although differ-
ences were not significant. Like in the other previous
studies, Nordqvist et al. [29] did not control for influ-
ential covariates including: (1) hormonal stimulation
[none, CC, follicle stimulating hormone (FSH) or CC+
FSH]; (2) smoking habits (2.8 % of lesbians and 9.2 % of
heterosexuals were smokers); (3) previous gynecological
problems (the incidence of several previous gynecological
problems in lesbians was at least twice as high as in het-
erosexuals); (4) number of prior treatments (lesbians had
previously undergone D-IUI and D-IVF more often than
heterosexuals, whereas heterosexuals had previously
undergone ICSI with partner sperm more often than les-
bians); and (5) previous pregnancies/deliveries (heterosex-
uals exhibited higher incidence of previous deliveries than
lesbians). Women’s age was, however, homogenous in
both groups (mean ± standard deviation: 32.4 ± 4 years).
D-IVF
Nordqvist et al. [29] compared success percentages be-
tween pair-bonded lesbians and pair-bonded heterosex-
ual women after fresh and frozen/thawed D-IVF
(Table 1). On this occasion, pregnancy percentage per
fresh D-IVF cycle (34.6 % versus 45.2 %) and per woman
after a mean number of ≈1.5 fresh D-IVF cycles (47.8 %
versus 68.7 %) were lower in the lesbian group. Live-
birth percentage per fresh D-IVF cycle (27.6 %, versus
33.3 %) and per woman after a mean number of ≈1.5
fresh D-IVF cycles (38.0 % versus 50.6 %) were also
lower in the lesbian group although differences were not
significant. These results contrast with the similar suc-
cess percentages obtained in frozen/thawed D-IVF cy-
cles. In particular, the pregnancy percentage per cycle
was 31.6 % versus 31.7 % and the pregnancy percentage
per woman after a mean number of ≈2 cycles was
63.3 % versus 64.7 % in the lesbian and heterosexual
group, respectively. Likewise, live-birth percentage per
frozen/thawed D-IVF cycle (24.5 % versus 23.1 %) and
per woman after a mean number of ≈2 frozen/thawed
D-IVF cycles (49.0 % versus 47.1 %) were also similar in
pair-bonded lesbians and pair-bonded heterosexuals.
Sampling bias, small sample sizes and inadequate use
of statistical methods to control for the effects of influ-
ential covariates may explain discrepancies in success
percentages of pair-bonded lesbians and pair-bonded
heterosexual women reported by Nordqvist et al. [29]
after D-IUI, fresh D-IVF and frozen/thawed D-IVF.
Success percentages of gays in gestational-surrogacy
programs
Like in lesbians after D-IUI, gays entering into gestational-
surrogacy programs tend to have higher success percent-
ages than heterosexual men (Table 2). Grover et al. [21]
reported that 56.8 % (21/37) of surrogate women recruited
by pair-bonded gays and 50.0 % (4/8) of surrogate women
recruited by single men (7 homosexuals and one hetero-
sexual) succeeded in achieving a pregnancy after a max-
imum of either two fresh cycles or one fresh and one
frozen transfer cycle. No significant differences in delivery
percentages per surrogate woman between the group of
pair-bonded gays/single men and a control group of het-
erosexual couples were evidenced (55.6 % versus 48.9 %).
Of note, this study did not control for the potential nega-
tive effects of male reproductive aging on semen parame-
ters and embryo/fetal development (for review, see [39]).
Furthermore, the study did not provide any information
about epidemiological data of heterosexual couples, oo-
cyte donors and gestational carriers including ovarian
stimulation protocol and medical indications for using
gestational surrogacy.
These deficiencies were partially amended in a recent
study by the same group [22]. This study reported the
largest gestational surrogacy series published so far (333
consecutive gestational surrogacy cycles including cycles
from most of the pair-bonded gays and single men pre-
viously reported by Grover et al. [21]). On this occasion,
the medical indications of heterosexual couples for using
gestational surrogacy were specified. Notwithstanding,
data analysis were either not controlled for ovarian
stimulation protocol and age of intended parents, oocyte
donors and gestational carriers. In addition, the group of
heterosexual couples was not homogeneous. In fact,
intended heterosexual parents used donor oocytes in
39.5 % (107/271) of cycles (mean age of oocyte donors:
26.2 years) whereas in the remaining 60.5 % (164/271) of
cycles (mean women’s age: 36.1 years) they used their
own (autologous) oocytes. Furthermore, the group of
heterosexual couples included a total of 17 cycles in
which embryos were concurrently transferred to both
the intended-parent woman and the gestational carrier.
In contrast, all the 52 pair-bonded gays/single men
Tarín et al. Reproductive Biology and Endocrinology (2015) 13:52 Page 5 of 7

entered into the study used exclusively donor oocytes
and gestational carriers.
The sampling asymmetries/biases between groups may
explain, at least in part, the higher, although not statisti-
cally significant, pregnancy percentage per cycle evi-
denced in the “pair-bonded gays/single men”group
(59.7 %) compared with a “failed to carry”(50.0 %) and a
“cannot carry pregnancy”(54.0 %) group. Likewise, the
“pair-bonded gays/single men”group displayed lower
miscarriage percentages per pregnant surrogate woman
(10.8 %) than the “failed to carry”(25.8 %) and the “can-
not carry pregnancy”(20.0 %) group, although differ-
ences among groups were not statistically significant.
Concluding remarks
The present review shows that lesbians after D-IUI and
gays entering into gestational-surrogacy programs tend
to have higher success percentages than heterosexuals.
This trend is not surprising if we take into account that
lesbians usually enter into D-IUI programs and gays into
gestational-surrogacy programs to fulfill their wishes to
have and raise their own offspring and create families,
not because they are infertile. However, the only single
study published so far on success percentages of lesbians
after D-IVF [29] provides puzzling results. In particular,
data show that pair-bonded lesbians have lower preg-
nancy and live-birth percentages than pair-bonded het-
erosexual women in fresh D-IVF cycles. In contrast,
pregnancy and live-birth percentages are similar in fro-
zen/thawed D-IVF cycles. Of note, all the reports
reviewed in the present study are methodologically
flawed because of sampling bias, small sample sizes and
inadequate use of statistical methods to control for the
effects of influential covariates including age, smoking
habits, previous gynecological problems, hormonal
stimulation type and protocol, and number of prior
treatment types and pregnancies/deliveries. Clinicians,
reproductive biologists and editors of fertility/infertility
journals should make efforts to prevent these deficien-
cies in future data reporting.
Abbreviations
CC: Clomiphene citrate; D-IUI: Intrauterine insemination with donor
spermatozoa; D-IVF: In-vitro fertilization with donor spermatozoa; FSH: Follicle
stimulating hormone; HIV: Human immune virus; hMG: Human menopausal
gonadotropins; ICSI: Intracytoplasmic sperm injection; IUI: Intrauterine
insemination; IVF: In-vitro fertilization; PCOS: Polycystic ovary syndrome.
Competing interests
The authors declare that they have no competing interests.
Authors’contributions
JJT has been involved in conception and design, acquisition, analysis and
interpretation of data, drafting the article and final approval of the version to
be published. MAGP and AC have been involved in analysis and
interpretation of data, revising the article critically for important intellectual
content and final approval of the version to be published.
Author details
1
Department of Functional Biology and Physical Anthropology, Faculty of
Biological Sciences, University of Valencia, Burjassot, Valencia 46100, Spain.
2
Department of Genetics, Faculty of Biological Sciences, University of
Valencia, Burjassot, Valencia 46100, Spain.
3
Research Unit-INCLIVA, Hospital
Clínico de Valencia, Valencia 46010, Spain.
4
Department of Pediatrics,
Obstetrics and Gynecology, Faculty of Medicine, University of Valencia,
Valencia 46010, Spain.
5
Service of Obstetrics and Gynecology, University
Clinic Hospital, Valencia 46010, Spain.
Received: 2 March 2015 Accepted: 27 May 2015
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