The mediating role of gestational diabetes mellitus in the associations of maternal prepregnancy body mass index with neonatal birth weight.

Background: Both prepregnancy obesity and gestational diabetes mellitus (GDM) have been linked to adverse neonatal birth weight. However, the mediating role of GDM between prepregnancy obesity and neonatal birth weight is unclear.

Method: The cohort study included 17 260 singleton pregnant women and their newborns. Participants' demographic characteristics, disease history, family history of the disease, and the perinatal outcomes were recorded. The association between maternal prepregnancy body mass index (BMI) status and small for gestational age (SGA) or large for gestational age (LGA) neonates was analyzed using logistic regressions, before and after adjusting for covariates and GDM. The potential mediation of GDM on the association between prepregnancy BMI and adverse birth weight was examined.

Result: Multivariate logistic regression demonstrated that prepregnancy underweight women were more likely to deliver SGA neonates compared to those who had normal weights, whereas prepregnancy obese pregnant women were more likely to have LGA neonates. The RMediation analyses illustrated that the mediation effect of GDM on the maternal prepregnancy BMI (continuous variable) and the risk of SGA was not significant, whereas the association between prepregnancy BMI and LGA was statistically mediated by GDM (95%CI of a*b: 0.009-0.051). The Iacobacci (2012) method indicated that the impact of maternal prepregnancy overweight (Zmediation = 2.418, P = .015) and obesity (Zmediation = 2.165, P = .030) on LGA was partially mediated by GDM, with an indirect effect of 16.3% and 13.1%, respectively.

Conclusion: Prepregnancy BMI was observed to be associated with SGA and LGA. The association of prepregnancy overweight and obesity with LGA was found to be partially mediated by GDM.