Gestational Diabetes Mellitus as an Effect Modifier of the Association of Gestational Weight Gain with Perinatal Outcomes: A Prospective Cohort Study in China.

The association of gestational weight gain (GWG) with perinatal outcomes seems to differ between women with and without gestational diabetes mellitus (GDM). Whether GDM is an effect-modifier of the association has not been verified. This study aimed to assess the modifying effect of GDM on the association of GWG with perinatal outcomes. Data on 12,128 pregnant women (3013 with GDM and 9115 without GDM) were extracted from a prospective, multicenter, cohort study in China. The associations of total and trimester-specific GWG rates (GWGR) with perinatal outcomes, including small size for gestational age, large size for gestational age (LGA), preterm birth, cesarean delivery, and gestational hypertension disorders, were assessed. The modifying effect of GDM on the association was assessed on both multiplicative and additive scales, as estimated by mixed-effects logistic regression. As a result, total GWGR was associated with all of the perinatal outcomes. GDM modified the association of total GWGR with LGA and cesarean delivery on both scales (all p < 0.05) but did not modify the association with other outcomes. The modifying effect was observed in the third trimester but not in the first or the second trimester. Therefore, maternal GWG is associated with perinatal outcomes, and GDM modifies the association with LGA and cesarean delivery in the third trimester.