Maternal cortisol and offspring birthweight: results from a large prospective cohort study

Maternal psychosocial problems may affect fetal growth through maternal cortisol. This large prospective cohort study examined among 2810 women (1) the association of maternal cortisol levels with offspring birthweight and small for gestational age (SGA) risk and (2) the mediating role of maternal cortisol on the relation between maternal psychosocial problems and fetal growth. Pregnant women in Amsterdam were approached during their first prepartum visit (+/-13 weeks gestation). Total maternal cortisol level was determined in serum and maternal psychosocial indicators were collected through a questionnaire. Maternal cortisol levels were negatively related to offspring birthweight (B=-0.35; p<.001) and positively to SGA (OR=1.00; p=.027); after adjustment (for gestational age at birth, infant gender, ethnicity, maternal age, parity, BMI, and smoking), these effects were statistically insignificant. Post hoc analysis revealed a moderation effect by time of day: only in those women who provided a blood sample < or =09:00h (n=94), higher maternal cortisol levels were independently related to lower birthweights (B=-0.94; p=.025) and a higher SGA risk (OR=1.01; p=.032). Maternal psychosocial problems were not associated with cortisol levels. In conclusion, although an independent association between maternal cortisol levels in early pregnancy and offspring birthweight and SGA risk was not observed, exploratory post hoc analysis suggested that the association was moderated by time of day, such that the association was only present in the early morning. The hypothesis that maternal psychosocial problems affect fetal growth through elevated maternal cortisol levels could not be supported.