Risk for fetal malformations and unfavorable neonatal outcomes in early-onset gestational diabetes mellitus.

Background: Early-onset gestational diabetes mellitus (GDM) is diagnosed before the 24th gestational week. Since early GDM is associated with first trimester hyperglycemia, many clinicians treat these women as having pre-GDM. However, whether early GDM increases the risk for unfavorable pregnancy outcomes and particularly for fetal malformations to a greater extent than late-onset GDM were not studied sufficiently. We aimed to examine the effect of early-onset GDM on unfavorable pregnancy outcomes.

Methods: A retrospective cohort study of women with GDM delivering singletons during 2005-2018 was conducted. Women were divided into GDM diagnosed at the first (Trimester1; up to 13.6 weeks; N = 117), the second (Trimester2; up to 23.6 weeks; N = 126), and the third trimester (Trimester3; N = 2334). The primary outcomes were neonatal malformations and a composite of large-for-age newborns, hypoglycemia and hyperbilirubinemia treated with phototherapy. Comparisons were made between early- (Trimester1 + Trimester2-groups) and late-onset GDM (Trimester3-group), and between the three trimesters.

Results: Fetal malformations were low and comparable between the trimester1, trimester2, trimester3 groups (2 (1.7%), 3 (2.4%), and 110 (4.7%), respectively). The composite neonatal complications was similar between the groups (68 (58%), 58 (46%), and 1087 (47%), respectively). In early-onset, the rates of neonatal hypoglycemia and shoulder dystocia were higher than in the late-onset GDM group (OR 95% CI 3.5 [2.0-6.1] and 10.3 [2.4-44.6], respectively). Macrosomia was higher in trimester1 compared with trimester2 and trimester3 cohorts (OR 95% CI 5.3 [1.7-16.9] and 2.8 [1.5-5.2], respectively).

Conclusions: The risk for fetal malformations was low and comparable between the first, second and third trimester GDM. Since the risks for macrosomia, shoulder dystocia, and neonatal hypoglycemia are higher in early-onset GDM, these women should undergo strict glycemic control, intensive monitoring, and careful neonatal evaluation.