Steroid Hormones in Cord Blood Mediate the Association Between Maternal Prepregnancy BMI and Birth Weight: Prepregnancy BMI, Steroid Hormones, and Birth Weight

OBJECTIVE: Maternal overweight has been associated with increasing offspring birth weight, but epidemiological data on potential biological mechanisms are limited. This study aimed to examine whether steroid hormones mediate the association between maternal prepregnancy BMI (pre-BMI) and birth weight. METHODS: This study involving 2,039 participants was conducted from an ongoing cohort study in Wuhan, China. Mediation analysis was used to identify the extent to which steroid hormones mediated associations. RESULTS: Each one-unit increase in pre-BMI was significantly associated with lower log2 -transformed cord blood levels of cortisol and corticosterone. Levels of cortisol and corticosterone were also negatively associated with birth weight. It was estimated that corticosterone mediated 3.48% of the association between pre-BMI and birth weight, and no significant mediation effect was observed in cortisol. After stratification by maternal gestational weight gain (GWG; within or in excess of the Institute of Medicine [IOM] guidelines), the associations of pre-BMI with cortisol and corticosterone levels were significant in the women with GWG > IOM but not in women with GWG ≤ IOM. When the mediation analysis in the women with GWG > IOM was limited, the mediation effects of cord blood cortisol and corticosterone were both significant (P < 0.05). CONCLUSIONS: Cord blood cortisol and corticosterone partially mediate the association of increased maternal pre-BMI with higher birth weight.