Background

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

Method

The cohort study included 17260 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 BMI status and small for gestational age (SGA), large for gestational age (LGA) neonates were analyzed using logistic regressions, before and after adjusting for covariates and GDM. The potential mediation of GDM on the association between pre-pregnancy BMI and adverse birth weight was examined.

Result

Multivariate logistic regression demonstrated that pre-pregnancy underweight women were more likely to deliver SGA neonates compared to those who had normal weights, whereas, pre-pregnancy obese pregnant women were more likely to have LGA neonates. The RMediation analyses illustrated that the mediation effect of GDM on the maternal pre-pregnancy BMI (continuous variable) and the risk of SGA wasn't significant, while the association between pre-pregnancy BMI and LGA was statistically mediated by GDM (95%CI of a*b: 0.009-0.051). The Iacobacci's (2012) method indicated that the maternal pre-pregnancy overweight (Zmediation= 2.418, p=0.015) and obesity (Zmediation= 2.165, p=0.030) on LGA were partially mediated by GDM, with an indirect effect of 16.3% and 13.1%, respectively.

Conclusion

Pre-pregnancy BMI was observed to be associated with SGA and LGA. The association of pre-pregnancy overweight and obesity with LGA was found to be partially mediated by GDM.