Objective Define the prevalence of OSA in a population of obese pregnant women. Secondary objectives were to assess its obstetric consequences and define its risk factors in this population. Methods This single-center prospective study took place at the Lille University Hospital from 2010 to 2016 and included pregnant women with a body mass index (BMI) > 35 kg/m2. They underwent polysomnography (type 1 sleep testing) between 24 and 32 weeks of gestation to diagnose OSA. Clinical, obstetric, and fetal data were collected monthly and at delivery. We compared the groups with and without OSA and calculated its prevalence. Results This study included 67 women with a mean BMI of 42.4 ± 6.2 kg/m2. Among them, 29 had OSA, for a prevalence of 43.3% (95% confidence interval, 31.4–55.2); it was mild or moderate in 25 women and severe in 4. Comparison of the two groups showed that women in the OSA group were older (31.9 ± 4.7 years vs 29.5 ± 4.8 years, P = .045), had chronic hypertension more frequently (37.9% vs 7.9%, P = .0027), and had a higher mean BMI (43.8 ± 6.2 kg/m2 vs 41.2 ± 6 kg/m2, P = .045). During pregnancy, they developed gestational diabetes more often (48.3% vs 23.7%, P = .04). No significant differences were observed for any of the other criteria studied. Conclusions The prevalence of OSA was high in our study, and women with it developed gestational diabetes during pregnancy more often. No other obstetric complications were observed.