Outcomes after 39 weeks among pregnant patients with diet-controlled gestational diabetes mellitus.

OBJECTIVE: To compare perinatal outcomes for patients with diet-controlled gestational diabetes mellitus (GDM), based on advancing gestational age at delivery. METHODS: Retrospective cohort study including patients delivering singleton, live born infants at ≥39 weeks' gestation between November 2010 and February 2024. Among patients with diet-controlled GDM at the time of delivery, perinatal outcomes were compared based on delivery timing, then compared to patients without diabetes. Statistical analyses included Mantel-Haenszel and Breslow-Day tests. RESULTS: Of 156,214 total deliveries, 4467 were to patients with diet-controlled GDM at ≥39 weeks. When comparing deliveries at ≥41 weeks to those at 39 weeks, odds of primary cesarean delivery (CD) (adjusted odds ratio [aOR], 1.55; 95% confidence interval [CI], 1.22, 1.97), forceps delivery (aOR, 1.41; 95% CI, 1.27, 1.58), third- and fourth-degree lacerations (aOR, 1.51; 95% CI, 1.32, 1.72), shoulder dystocia (aOR, 1.87; 95% CI, 1.49, 2.36), large for gestational age (LGA) infants (aOR, 1.48; 95% CI, 1.19, 1.83), and brachial plexus injury (aOR, 2.10; 95% CI, 1.53, 2.87) were higher after adjusting for age and parity. When compared to patients without diabetes, patients with diet-controlled GDM experienced higher rates of most examined outcomes, but the rate of increase with advancing gestational age was not higher, except for primary CD and LGA infants (Breslow-Day p = 0.03 and 0.09, respectively). CONCLUSION: Patients with diet-controlled GDM have increased perinatal risks compared to those without GDM, which rise with advancing gestational age after 39 weeks. The risk of primary CD and LGA infants with advancing gestational age is exaggerated for patients with diet-controlled GDM.