To date, this study is the most comprehensive evaluation of the associations between prenatal maternal sex steroid hormones and fetal/infant growth with 4 major sex steroid hormones measured in all trimesters and 4 timepoints of infant anthropometric assessments. Our findings reveal the complex interplay between prenatal sex steroid hormones, birth size, and postnatal growth, with implications for understanding the developmental origins of childhood obesity. Notably, the associations between prenatal sex steroid hormones and both birth size and postnatal growth were found to vary by the specific individual sex steroids and the timing of pregnancy. Furthermore, the study uncovered significant sex differences in these associations, suggesting potential underlying mechanisms that may differ between male and female infants. Importantly, the observed associations between prenatal sex steroid hormones and postnatal weight and adiposity growth were beyond birth size, underscoring the unique role of prenatal sex steroids in shaping later childhood growth.
Specifically for birth size, our finding of the positive association between 3rd trimester E3 and birthweight aligned with prior findings (16, 17, 19–21). However, limited research has explored the associations of other sex steroid hormones with birthweight, as well as their interactions with infant sex. To our knowledge, the associations between prenatal sex steroid hormones and neonatal adiposity have not been investigated, although neonatal adiposity has been linked to later childhood obesity (3). This study found that 1st trimester E1 and E2 were associated with increased birthweight and neonatal TST in female infants after adjustment of early-pregnancy BMI. Two prior studies assessing 1st trimester E2 reported inconsistent results, with one only assessing female infants and showing a similar but non-significant trend of birthweight (21), and the other finding no associations with birthweight without assessing sex differences (24). Hence, early-pregnancy E1/E2 is potentially associated with fetal growth in female infants, which warrants further investigation.
Additionally, we observed that fT, the bioactive form of TT, in the 2nd trimester were positively associated with birthweight in male infants, while the associations were reversed in the 3rd trimester. TT showed similar trends as fT. The association of 3rd trimester, but not 2nd trimester, testosterone with birthweight was consistent with previous findings (23, 25, 38). But a prior study found higher 2nd trimester TT was associated with lower birthweights in infants of both sexes (23). Contrary to the associations with birthweight, 3rd trimester TT and fT were positively associated with neonatal TST in both sexes in this study. These findings underscored the need for further investigation into the specific relationships between prenatal sex steroid hormones and birth size, while considering sex-specific associations and the timing of hormone exposure.
For weight growth trajectories during infancy, unlike the limited previous research, which predominantly focused on 3rd trimester sex steroid hormones (16, 25, 26), this study assessed multiple sex steroid hormones across pregnancy. Additionally, the associations with infant adiposity growth trajectories were assessed in this study, as infant adiposity has been associated with childhood adiposity and cardiovascular risks (39). Specifically, a negative association between 3rd trimester E3 and the declining WFA trajectory observed in this study contrasted with a prior study that found a correlation between E3 and children’s weight at two years of age (16). This difference in findings might be attributed to the prior study’s focus on weight rather than weight trajectories and its lack of adjustment for birthweight. Additionally, this study found that associations between 1st trimester E1 and E2 and WFA growth trajectories were stronger in male infants. Also, dynamic associations were observed between E1 in the 2nd and 3rd trimesters with postnatal TST changes in infants of both sexes.
With regards to testosterone, sex differences were evident in the associations between TT/fT and postnatal growth independent of birth size. Particularly, 1st and 3rd trimester TT/fT tended to be associated with a lower probability of the declining (W2), accelerating (W3), and high stable (W4) WFA trajectories compared to the low stable WFA trajectory (W1) in male infants, while the associations were reversed in relation to 2nd trimester TT/fT. Two prior studies primarily focused on 3rd trimester TT and androgen activity, with one study in a small sample (n = 49) reporting a positive association with rapid weight gain (birth to 6 months) in male infants (25), and the other identifying an association with a higher probability of an accelerated catch-up growth pattern compared to a consistent high weight pattern in male children (26). We observed a similar trend of 3rd trimester TT with a high probability of accelerating WFA trajectory (W3) compared to high stable WFA trajectory (W4) in male infants (not shown). Interestingly, the associations between prenatal testosterone and postnatal TST trajectories were more noticeable in female infants. Overall, these findings emphasized the importance of considering longitudinal growth patterns, sex-specific differences, and controlling for birth size when assessing the impact of prenatal hormone exposure on postnatal growth with potential implications for understanding the developmental origins of childhood obesity.
The findings of this study underscored the multifaceted mechanisms potentially involved in the role of prenatal hormone exposure in fetal and postnatal growth. During early pregnancy, E1 and E2, the primary estrogens (40), stimulate angiogenesis, vascularization, blood flow in myometrial and placental arteries, and facilitating nutrient transportation from the placenta to the growing fetus through regulating uteroplacental expression of glucose transporters.(9, 10). During mid-late pregnancy, E3 is mainly synthesized by the placenta from dehydroepiandrosterone sulfate produced by fetal adrenal glands after 10 weeks of gestation and becomes the principle estrogen (16, 40). Therefore, E3 is an indicator of the function of placental sulfatases and fetal adrenal glands, which has been postulated to reflect fetal well-being (16, 41). E3 has also been proposed to regulate uteroplacental vascularization and blood flow in late pregnancy, but its full physiological function remains to be elucidated (42). Regarding postnatal growth, estrogens have been found to interact with several epigenetic enzymes and regulate epigenetic modifications (12, 43). Particularly, prenatal E3 exposure affects epigenetic modification in brain, muscle, and adipose tissues that may be involved in postnatal adiposity and growth (12).
We observed sex-specific difference in the associations between prenatal testosterone exposure and fetal and postnatal growth and adiposity. The role of 2nd trimester testosterone appeared to differ from that of testosterone in the 1st and/or 3rd trimesters. These variations in infant sex and timing of pregnancy may be attributed to the peak fetal testosterone production in late 1st and early 2nd trimesters in male fetuses (44). Testosterone of fetal origin may promote musculoskeletal development in male fetuses during this stage (45). However, testosterone of maternal origin downregulated placental amino acid transport activity in a rat model (11). Also, maternal testosterone reduced uterine artery blood flow and affected placental vasculature particularly in male rat fetuses (46). This evidence could explain how high maternal testosterone levels were associated with lower birthweight, particularly in male fetuses. Furthermore, testosterone has been implicated in promoting visceral preadipocyte proliferation and adiposity in human (13, 47), with sex-specific responses likely influenced by sex dimorphism in adipose tissue biology, such as differential expression of sex steroid receptors in adipose tissue, the number of adipocyte precursor cells, and differential programming by sex chromosome (27). Additionally, testosterone interacts with epigenetic enzymes and can regulate epigenetic modifications (48), potentially influencing postnatal growth and adiposity. Finally, postnatal endogenous testosterone production in male infants before 6 months of age may contribute to sex differences in postnatal growth (49). The association between prenatal maternal and postnatal infant testosterone levels remains unclear and warrants further investigation. If maternal hormones play a role in programming the developing infant hormone axis during pregnancy, it may offer another mechanism for understanding associations between prenatal maternal sex steroids and postnatal infant size.
The strengths of this study include: (1) the prospective repeated measures of the major estrogens and testosterone across all three trimesters; (2) sensitive LC-MS/MS and equilibrium dialysis method were used to quantify estrogens and testosterone, particularly the low concentrations of E3 in early pregnancy and testosterone across pregnancy; (3) by using path analysis models and including interactions with infant sex, we were able to estimate direct associations of sex steroids in three trimesters simultaneously, giving insight into sensitive periods of hormone exposure and sex-specific responses; (4) birth size was adjusted in the models of postnatal growth, underscoring the role of prenatal sex steroid hormones in postnatal growth beyond birth size. Several caveats are important to consider when interpreting the findings of this study. We focused on estrogens and testosterone and did not assess additional prenatal hormones, such as dihydrotestosterone, and progesterone, that may mediate the role of estrogens and testosterone in fetal and postnatal growth (26). Also, the concentrations of fT were low, making them susceptible to methodological issues. Therefore, the results of fT should be interpreted alongside those of TT. Additionally, we used a relatively crude measure of adiposity, and more advanced tools, such as dual-energy x-ray absorptiometry, magnetic resonance imaging, or air displacement plethysmography may provide more accurate measures.