Impact of Maternal Thyroperoxidase Status on
Fetal Body and Brain Size
Roneé E. Wilson,1Hamisu M. Salihu,1,2Maureen W. Groer,3Getachew Dagne,1
Kathleen O’Rourke,1and Alfred K. Mbah1
1Department of Epidemiology and Biostatistics, College of Public Health, University of South Florida, 13201 Bruce B. Downs,
MDC56, Tampa, FL 33612, USA
2Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, College of Medicine, University of South Florida,
2 Tampa General Circle, STC, 6th Floor Tampa, FL 33606, USA
3College of Nursing, University of South Florida, 12901 Bruce B. Downs, MDC22, Tampa, FL 33612, USA
Correspondence should be addressed to Hamisu M. Salihu; email@example.com
Received 6 September 2013; Revised 5 November 2013; Accepted 23 November 2013; Published 29 January 2014
Academic Editor: Gary L. Francis
Copyright © 2014 Rone´ e E. Wilson et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
of maternal thyroid autoantibodies on infant outcomes. The objective of this study was to examine the influence of maternal
thyroperoxidase (TPO) status on fetal/infant brain and body growth. Six-hundred thirty-one (631) euthyroid pregnant women
analysis revealed maternal that TPO positivity was significantly associated with smaller head circumference, reduced brain weight,
and lower brain-to-body ratio among infants born to TPO+ white, non-Hispanic mothers only, distinguishing race/ethnicity as
an effect modifier in the relationship. No significant differences were noted in body growth measurements among infants born to
TPO positive mothers of any racial/ethnic group. Currently, TPO antibody status is not assessed as part of the standard prenatal
care laboratory work-up, but findings from this study suggest that fetal brain growth may be impaired by TPO positivity among
prenatal thyroid treatment is warranted.
Thyroid dysfunction is one of the most common endocrine
disorders in women of childbearing age , second only to
diabetes mellitus. Approximately 2-3% of women are diag-
nosed prenatally with abnormal thyroid function; however, a
greater number may go undetected due to lack of consensus
on testing and treatment modalities during pregnancy [2–
4]. Normal maternal thyroid function is critical for early
fetal development, as the fetus does not produce thyroid
hormones until the end of the first trimester (∼12–14 weeks
dysfunction, particularly hypothyroidism, during pregnancy
gestation) and, prior to that time, is solely dependent on
the mother’s hormone supply [5–7]. The impact of thyroid
is well documented [8, 9], and the associated adverse
fetal/infant outcomes range from preterm delivery to fetal
death [10–14]. Abnormal maternal thyroid hormone levels
during gestation are also linked to long-term effects in older
A number of women may be biochemically euthyroid or
exhibit thyroid hormone levels within normal limits but test
positive for thyroid autoantibodies such as thyroperoxidase
(TPO) antibody. In fact, it is estimated that 10% of pregnant
women are TPO positive ; however, fewer studies have
among euthyroid mothers. Limited research tends to suggest
that TPO positivity, independent of abnormal thyroid levels,
Hindawi Publishing Corporation
Journal of yroid Research
Volume 2014, Article ID 872410, 8 pages
2 Journal of Thyroid Research
may increase the risk of placental abruption, spontaneous
miscarriage, and perinatal death [11, 13, 18–24]. Even fewer
studies have assessed the impact of maternal TPO antibody
status on infant specific variables such anthropometric mea-
surements at delivery although these studies have produced
between maternal autoantibody status and infant outcomes,
this study uniquely examined the influence of maternal TPO
status on fetal/infant brain growth at delivery, which has
been linked to cognitive function in childhood [26, 27]. This
project was undertaken with the following hypotheses: (1) at
delivery, newborns of TPO+ mothers will exhibit impaired
body growth as indicated by reduced birth weight and birth
length; (2) at delivery, infants born to TPO+ mothers will
exhibit impaired brain growth as exhibited by reduced head
circumference and calculated brain weight.
2.1. Participants. Pregnant women (푁 = 631) were recruited
were eligible for participation in the study if they were
between 18 and 45 years of age, 16 to 25 weeks gesta-
tion, able to understand and speak the recruiter’s language
(English or Spanish), and essentially healthy without plans
to terminate the pregnancy or relocate prior to 6 months
postpartum. Exclusion criteria included known autoimmune
disease, previous thyroid disease, presence of chronic dis-
from prenatal clinics in Tampa, Florida, and the surrounding
area between November 2007 and December 2010. Women
immunity, mental illness, body mass index (BMI) <20, cur-
biochemically euthyroid. Thyroperoxidase antibody status
was measured for all participants at the time of enrollment
and women were classified as TPO positive or negative.
Thyroid stimulating hormone (TSH) levels were measured
for all TPO positive women at the time of enrollment.
The study was approved by the University of South Florida
Institutional Review Board. All participants gave full written
rent multiple gestation, current pregnancy product of invitro
fertilization (IVF), and fetal abnormalities. All women were
2.2. Exposure Assessment. Thyroperoxidase antibody (TPO)
status was the exposure of interest. TPO status was deter-
mined in 631 plasma samples according to kit directions by
ELISA (ORGENTEC, Mainz, Germany) using standards and
controls. All samples were collected in duplicate and titers
recorded. The coefficient of variation was always less than
5%. TPO antibody titer greater than 20IUs/mL was used as
the cutoff value for determining positivity, since a value from
0 to 20 is considered within normal range . Based on
TPO titers, women were categorized as TPO positive or TPO
2.3. Outcome Assessment. Newborn anthropometric mea-
surements were retrieved from maternal delivery records
including ultrasound-derived gestational age in weeks, birth
weight (grams), birth length (centimeters (cm)), head cir-
cumference (cm), abdominal circumference (cm), and chest
and 9.4 ± 4.5, respectively.
circumference (cm). Infant head circumference at birth was
used to derive two additional indices of fetal brain size: brain
weight, and brain-to-body ratio (BBR). Brain weight was
estimated from the following formula: brain weight (g) =
0.037 × head circumference (cm)2.57, which is derived from
the National Institute of Neurological and Communicative
Disorders and Stroke’s Collaborative Perinatal Project .
Brain-to-body ratio (BBR) was defined as 100 × the ratio of
to reside in the brain. Since the brain weight is a function of
the head circumference, the formula could thus be rewritten
in terms of birth weight and head circumference as BBR =
the infant’s estimated brain weight to its birth weight. This is
the percentage of the infant’s birth weight that is estimated
100 × [0.037 × head circumference (cm)2.57]/birthweight (g).
lower percentage of birth weight residing in the brain .
Typical values for healthy infants are 9-10% .
A high BBR is indicative of a higher proportion of birth
weight residing in the brain, while a lower BBR indicates a
2.4. Study Sample. Delivery records for 52 participants were
not available at the time of analysis. For the current study,
multiple gestation pregnancies (푛 = 6) and pregnancies
resulting in fetal demise (푛 = 4) were excluded. To promote
delivered term infants. Figure 1 provides an overview of the
homogeneity of the sample and reduce confounding factors,
analysis was restricted to term infants only (≥37 weeks
2.5. Statistical Analysis. Maternal thyroid status was a cate-
sample 푡-test were used to assess differences in sociodemo-
graphic characteristics between TPO+ and TPO− mothers.
was used to demonstrate the influence of TPO status on
continuous outcomes such as birth weight, birth length, and
head circumference. The covariates in the regression models
were selected a priori based on information in the published
literature. These variables included maternal age, parity,
race/ethnicity (White Non-Hispanic; black non-Hispanic,
Hispanic and other), marital status, prenatal smoking habits,
prepregnancy body mass index (BMI), delivery type and
gender of the infant. Several variables were dichotomized in
marital status (married∗or unmarried), smoking habits
Mean differences in growth parameters were examined by
the regression models: parity (nulliparous∗or multiparous),
participants as the referent category.
A combination of graphic methods and statistical tests
were used to check for violations of the regression assump-
tions. After fitting the linear regression models to the data,
the residual normal QQ plots and by use of the Shapiro-Wilk
test. Visual inspection of residual scatter plots of outcome
variables and errors of prediction were evaluated to ensure
(smoker or nonsmoker∗), pre-pregnancy BMI (overweight
(BMI > 25) or nonoverweight∗), delivery type (vaginal∗or
estimates were derived in all cases by using TPO negative
the referent category for each variable. Additionally, adjusted
Journal of Thyroid Research3
N = 631
n = 6
n = 528
n = 470
n = 58
n = 4
n = 52
(<37 weeks gestation)
Figure 1: Diagram of study population.
that the homoscedasticity assumption was not violated.
Variance inflation and tolerance values were used to assess
multicollinearity. Data for all outcome variables in the study
sample were 99% complete. SAS version 9.3 (SAS Institute,
Cary, NC) was used to perform all analyses.
with a mean age of 28.03 ± 5.85 years (range 18–45). Nearly
The mean gestational age at delivery of the term infants
Thefinalstudysample(푛 = 528)comprisedpregnantwomen
retained in the sample was 39.02 ± 1.10 (range 37–41 weeks).
48% (푛 = 253) of the sample were white, 59% (푛 = 309)
with a mean TSH level of 1.46±1.12. Table 1 depicts selected
differ significantly from their negative counterparts in terms
of racial/ethnic background, marital status, smoking habits,
or body mass index. TPO+ mothers tended to be older in age
and were more likely to deliver female infants; however, nei-
of mean gestational age at delivery showed that white non-
Hispanic and Hispanic mothers were more likely to deliver
infants at 39+ weeks gestation compared to black mothers
and mothers in the “other” racial/ethnic category (data not
shown). No differences were noted in delivery type (vaginal
were married, and less than 6% (푛 = 30) were smokers.
Approximately 11% (푛 = 58) of the final sample tested
sociodemographic characteristics by maternal TPO status.
Women who tested positive for the TPO antibody did not
positive for the thyroperoxidase antibody during pregnancy
in mean newborn birth weight, birth length, abdominal cir-
cumference, or chest circumference were observed between
the two groups (Table 2). Nonetheless, small but significant
differences were noted for the mean head circumference
measurements among infants born to TPO+ mothers versus
resp.(푃 = 0.04)).Additionally,infantsborntoTPO+mothers
at delivery indicated that infants born to mothers who were
TPO+ had a smaller head circumference and reduced brain
TPO− mothers (34.45cm ± 1.34 SD versus 34.86cm ± 1.45,
had significantly smaller brain weight than those born to
weight (훽 = −407; standard error (SE) = 0.200; 푃 < 0.05
for lower brain-to-body ratio; however, the results were not
significant (Figure 2). Unadjusted analysis did not signify an
association between TPO status and newborn growth vari-
ables (birth weight, birth length, abdominal circumference,
or chest circumference).
Table 3 summarizes the adjusted multiple regression
results for fetal/infant brain growth variables. After adjust-
ing for several maternal and pregnancy factors including
maternal age, smoking habits, and infant weight at birth,
the relationship between TPO status and infant head cir-
cumference at birth was not significant in the overall pop-
ulation but was highly significant among infants born to
and 훽 = −10.307; SE = 5.001; 푃 < 0.05, resp.). Infants
born to mothers with TPO positivity also showed a tendency
4Journal of Thyroid Research
Table 1: Selected sociodemographic characteristics by TPO status of pregnant women in the study.
TPO positive (푁 = 58) TPO negative (푁 = 470)
Body mass index (BMI)
37 (63.79%) 272 (58.00%) 0.40
17 (29.82%) 148 (31.56%)0.79
2 (3.45%)28 (6.00%) 0.76
39 (67.24%) 301 (64.04%)0.63
Table 2: Selected infant characteristics at delivery by maternal TPO status.
TPO positive (푁 = 58) TPO negative (푁 = 470)
Gestational age at delivery
Head circumference (cm)
Abdominal circumference (cm)
Low birth weight (LBW)
Small-for-gestational age (SGA)
Large-for-gestational age (LGA)
white non-Hispanic mothers (훽 = −0.727; standard error
distinguishing race/ethnicity as an effect modifier in the
relationship between maternal TPO status and fetal brain
38.98 ± 1.02
39.04 ± 1.11
24 (41.38%) 241 (51.28%)0.15
Apgar < 7
Birth Length (cm)
High birth weight (HBW)
Birth weight (gm)
Chest circumference (cm)
(SE) = 0.214; 푃 < 0.001) and among those in the “other”
racial/ethnic group (훽 = −1.636; SE = 0.713; 푃 < 0.05),
fetal/infant brain weight persisted among infants whose
mothers were categorized in either the white non-Hispanic
or Other racial/ethnic groups. Table 3 also reflects that the
association between maternal TPO status and brain-to-body
Journal of Thyroid Research5
and gestational age at delivery.
∗∗and∗∗∗indicate significance at 0.05 and 0.01 level, respectively.
Overall 훽 (SE)White 훽 (SE)Black 훽 (SE)
Hispanic 훽 (SE)
Other 훽 (SE)
−0.237 (0.544)0.471 (0.268)
ΨAdjusted for maternal race/ethnicity, smoking habits, maternal age, marital status, parity, maternal obesity, delivery type, infant gender, infant birth weight,
†Adjusted for maternal race/ethnicity, smoking habits, maternal age, marital status, parity, maternal obesity, delivery type, infant gender, and gestational age.
Table 4: Regression results for fetal/infant body growth variables at delivery.
Birth length‡훽 (std.
†Adjusted for maternal race/ethnicity, maternal age, marital status, prenatal smoking habits, parity, prepregnancy body mass index, type of delivery, infant
gender, and infant length at delivery.
‡Adjusted for maternal race/ethnicity, maternal age, marital status, prenatal smoking habits, parity, prepregnancy body mass index, type of delivery, infant
gender, infant birth weight, and gestational age at delivery.
ratio was significant among infants born to TPO+ non-
Hispanic white mothers only. In this study population, birth
weight, birth length, abdominal circumference, and chest
This study examined the relationship between maternal
thyroid peroxidase antibody status and newborn brain and
body growth measurements within a cohort of euthy-
roid pregnant women. The findings indicate that maternal
race/ethnicity modifies the relationship between TPO pos-
itivity and reduced brain growth measurements at delivery
(head circumference, brain weight and brain-to-body ratio).
Upon closer examination, the relationship appears to be
the most noticeable among white non-Hispanic mothers.
Although this analysis indicates that TPO positivity may
result in impaired brain growth among infants of mothers
in the “other” racial/ethnic category, this finding should be
interpreted with caution due to the small sample size of this
subgroup (푛 = 37). However, it can be theorized that the
likely than their nonwhite counterparts to deliver later term
(39+ weeks gestation), thus allowing the differences in brain
growth variables to be more apparent [30, 31]. However,
nonwhite mothers have a tendency to deliver earlier term
infants who may not have had the opportunity to reach full
potential, thereby masking the effects of TPO influence.
The present analysis did not indicate a significant rela-
tionship between TPO status and infant birth weight in
this study sample. This finding is contradictory to those
differences in brain growth measurements are more marked
among white non-Hispanic infants because they are more
studies that have reported increased likelihood of low birth
weight infants born to TPO+ mothers  and an increased
likelihood of large-for-gestational age infants born to TPO+
women . Similar to previously published studies ,
this analysis did not find a difference in the birth length,
abdominal circumference, or chest circumference of infants
born to TPO+ mothers compared to those born to TPO−
Although measurement of thyroid antibodies does not
give any indication of thyroid function, the presence of TPO
antibodies may be associated with decreased thyroid func-
tional reserve during pregnancy [32, 33]. Reduced functional
within the normal reference range . Some researchers
hypothesize that the presence of TPO antibodies during
a time of increasing thyroid hormone demand such as
pregnancy implies that the mother may become hypothyroid
during gestation and that transient maternal hypothyroidism
may ultimately be responsible for the adverse outcomes [33,
35, 36]. However, previous studies have reported the detri-
mental effects of TPO antibodies independent of abnormal
thyroid hormone levels or disorders [13, 21]. Results of this
study support this assumption, as our findings indicate that
TPO antibodies are associated with reduced brain growth
measurements among infants born to a vulnerable subgroup
of euthyroid women.
A notable strength of this study is the prospective
design, as many of the previous studies were retrospective
in nature [10, 35, 37]. Additionally, laboratory analysis of
thyroid stimulating hormone (TSH) was used to confirm
6 Journal of Thyroid Research
Brain-body-ratioBirth weight Birth length
Beta coefficient and 95% CI
Figure 2: Unadjusted analysis of newborn brain and body growth variables at delivery (brain weight omitted from graph due to scaling
differences(훽 = −10.307(95%CI−20.130–−0.483)))(linearregressionbetacoefficientand95%confidenceinterval(CI)),TampaBay,Florida,
euthyroid state among participating mothers. The outcome
variables were extracted from maternal delivery records;
therefore, measurements were not influenced by knowledge
of maternal TPO status. One limitation of this study is the
lack of laboratory confirmed prenatal TSH data on women
in the TPO negative group. This group was presumed to
be euthyroid based on the absence of thyroid dysfunction
symptoms and the stringency of the study exclusion criteria
(e.g., no history of thyroid disease or autoimmune condi-
tions). However, it is unlikely that this limitation influenced
the study findings, as thyroid dysfunction in the TPO−
TPO positivity and fetal/infant brain growth. Additionally,
postpartum TSH levels were measured on a subsample of the
group would have biased the results toward the null and
participants resulting in mean values of 3.17±4.73 for TPO+
After controlling for several maternal and pregnancy
factors, TPO positivity was associated with smaller head
circumference, reduced brain weight and lower brain-to-
body ratio. However, the influence of TPO status on brain
growthwas modifiedby maternalrace. Futurestudies should
focus on the identification of genetic variants or single
interaction between maternal TPO status and race/ethnicity.
Epigenetic analysis may prompt ethnic-based screening for
TPO autoantibodies. This is potentially important because
findings from recent studies  indicate that substitu-
tive treatment with levothyroxine may lower the chance
of adverse obstetric outcomes (miscarriage and premature
for TPO autoantibodies.
Considering the long-term implications of impaired
fetal/newborn growth, it is important to identify avenues for
women (푛 = 47) and 2.05 ± 1.80 for TPO− women (푛 = 41),
thus providingadditionalevidence that the study sample was
status during pregnancy may be one of those factors that
play a role in fetal growth impairment but is currently being
overlooked due to lack of consensus on maternal testing and
treatment. At present, TPO antibody status is not assessed as
part of the standard prenatal care laboratory work-up, but
this study suggests that fetal brain growth may be impaired
with TPO positivity among certain populations; therefore,
autoantibody screening among high-risk subgroups may be
useful for clinicians to determine whether prenatal thyroid
treatment is warranted.
Conflict of Interests
The authors declare that there is no conflict of interests
regarding the publication of this paper.
This research was supported by a research diversity supple-
ment to a National Institutes of Health (NIH) Grant (R01-
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