The synergistic role of severe obesity and gestational diabetes mellitus (GDM) on pregnancy complications has been poorly studied. We aim to analyze the impact of GDM on pregnancy complications in women with class III obesity.

we performed a retrospective monocentric study including women with a pregestational BMI≥40kg/m2 with a singleton pregnancy from January 1996 to December 2014. We compared the risks of maternal, fetal and neonatal complications between patients with GDM and those without GDM.

We included 354 patients, 121 (34.3%) had GDM and 63 needed insulin treatment (52.9% of the GDM women). Patients with GDM were older (30.4±5.1 vs 28.9±4.8 years,p=0.008) and had more frequently a history of GDM (24.8% vs 6.1%; p<0.0001). Patients with GDM were more often hospitalized (47.8% vs 29.8%, p=0.001) and were more likely to have premature birth (11.7% vs. 5.3%, p=0.031). Neonates from mothers with GDM were more frequently large for gestational age (31.6% vs 19.4%, p=0.011), and had a higher rate of transfers to neonatal intensive unit (9.2% vs 4.0%, p=0.047). There was no difference for preeclampsia, C-section, shoulder dystocia, neonatal hypoglycemia or postpartum complications. Outcomes were comparable in women with or without insulin therapy.

The rate of GDM is particularly high in class III obese women. Morbidly obese women with GDM were more at risk for complications and needed more often insulin therapy. Our results suggest to pay a particular attention in this high-risk population.