The gender-specific association between maternal prenatal stress and offspring emotional and behavioral health has been fully summarized . Studies from animal models indicated that gender-dimorphic placental glucocorticoid response genes to prenatal stress may provide the underlying mechanism [23, 24]. However, evidence from human studies is lacking. Our population-based perspective cohort study found that pregnancy-related anxiety at the third trimester could affect emotional symptoms only in girls and hyperactivity only in boys of preschool age, which confirms and extends our previous research [7, 8]. Furthermore, only boys showed differential methylation of the FKBP5 gene in response to prenatal pregnancy-related anxiety; also, methylation of NR3C1 and HSD11B2 genes was associated with the risk of emotional symptoms and hyperactivity only in boys. To the best of our knowledge, this is the first human evidence to indicate that gender-specific effects of maternal pregnancy-related anxiety during pregnancy on preschoolers’ neurobehavior depended upon the gender-dependent DNA methylation patterning of placental genes that regulate fetal exposure to glucocorticoids.
We add to the literature  by showing similar findings in pregnancy-related anxiety, a special mode of prenatal stress that has received little attention but predicts fetal development outcomes more accurately than general anxiety and depression symptoms [40, 41]. Compared with our two previous works [7, 8], the present study found similar gender-dependent outcomes but only focused on pregnancy-related anxiety at the third trimester because this cohort data showed that the third trimester is the critical period of pregnancy-related anxiety on child neurobehavioral development . However, a small sample size (n = 27) study showed that higher pregnancy-related anxiety symptoms were significantly associated with more emotional symptoms in boys compared to girls at 4 years old . Thus, compared with the male-bias hyperactivity, the female-bias relationship of pregnancy-related anxiety with emotional symptoms needs to be further explored.
Our results partly support our hypothesis by finding that only boys showed differential methylation of the FKBP5 gene in response to prenatal pregnancy-related anxiety; also, only in boys was the methylation of NR3C1 and HSD11B2 genes associated with the risk of emotional symptoms and hyperactivity, although no mediating effects were found. To date, there has been two human studies investigating a gender-specific association mechanism through the placental glucocorticoid signaling pathway[18, 43]. In Stroud et al. study, although the decrease of HSD11B2 methylation in placenta was found to be associated with increased baseline cortisol in infants of mothers with prenatal major depression disorder, no gender difference was found in HSD11B2 methylation in the placenta . Besides, work from Green et al. that focused on American mothers suggested that the correlation between methylation and expression of the HSD11B2 gene in human placenta with infant birth weight was found only in female and not male infants . The role of methylation of cortisol regulation genes in placenta in the gender-specific association between prenatal stress and child outcomes needs to be further explored.
Pregnancy-related anxiety contributes to neurological behavior in children through DNA methylation of genes regulating glucocorticoids, possibly based on the ethnicity of the study population or their living environment . For example, a prospective cohort study with 61 American women revealed that modestly elevated placental CpG methylation of FKBP5 was associated with lower fetal coupling (the cross-correlation between fetal movement and heart rate, providing an index of fetal CNS development) , but we found no association between FKBP5 methylation and neurobehavioral outcomes in our present study, which focused on pregnant Chinese women. Furthermore, Grasso et al. found that infant saliva FKBP5 methylation correlated with maternal post-traumatic stress disorder symptoms during pregnancy, but only in infants with the homozygous FKBP5 rs1360780 C allele . In addition, Capron et al. performed a multi-ethnic study and found that placental gene expression of NR3C1 and HSD11B2 is regulated by maternal prenatal anxiety and prenatal life events, but only in Caucasians, instead of South Asians and African/African-Americans . Our data also showed no links between prenatal anxiety and placental NR3C1 and HSD11B2 methylation in Chinese. Thus, it is necessary to understand more about the role of social and biological differences in the mechnism of prenatal stress and psychopathology in the rest of the world, apart from the already most research Caucasian samples from high-income countries.
The current study had additional strengths that lend confidence to the findings. Firstly, this is a prospective cohort study with a good strength of causal reasoning, a relatively high response rate of participants and, by controlling multiple confounding factors (e.g. maternal and child characteristics and infant breastfeeding), thus the role of pregnancy-related anxiety on children’s development was detected more accurately. Secondly, pregnancy-related anxiety may be a more accurate predictor of adverse birth outcomes and child health than general anxiety . Instead of using tools designed for the general population to assess pregnancy-related anxiety, such as the State-Trait Anxiety Inventory (STAI), our approach may be more accurate because it includes items specific to the mother’s experience during pregnancy . Thirdly, the gender-specific mechanism from the glucocorticoid signaling pathway in placenta [21, 22, 14, 46, 10, 47] has been well-documented but our study goes one step further to estimate the intrauterine environment by comparing research focused on fetal saliva or flooding of cortisol .
Although novel, this study has some limitations that should be taken into account. Firstly, for the prenatal stress assessment we just assessed pregnancy-related anxiety and did not include other modes of prenatal stress (e.g. life events, depression) or stress at postpartum; these forms of stress, which also predict child behavioral and emotional development, were therefore not controlled during our analysis [49, 50]. Secondly, our data showed that hyperactivity is more common among males (male:female = 19.4:13.2%; P < 0.05) and we cannot rule out the possibility that there is more scope to detect associations between pregnancy-related anxiety and hyperactivity in males. Thirdly, we used factor analysis, which is a statistical technique that use the idea of dimensionality reduction to describe variability among a number of measured, correlated variables as a lower number of latent factors, in order to reduce the number of comparisons made. Although the cumulative contribution rate of the extracted 5 factors was relatively high (73.8%), the explained variance is small if many loci are combined in one factor. Lastly, there are also other important gender-specific modes of maternal–fetal stress transfer, such as placental inflammation , and additional research is required to determine how perturbations in stress-related biological responses conspire to influence poor offspring outcomes.