OBJECTIVE: To investigate the associations between obstructive sleep apnea (OSA) and maternal and neonatal morbidities in a cohort of obese gravid women. METHODS: Participants were enrolled in a prospective observational study designed to screen for OSA and describe the possible risk factors for and outcomes of OSA among obese (body mass index [BMI, calculated as weight (kg)/[height (m)](2)] 30 or higher) pregnant women. Women underwent an overnight sleep study using a portable home monitor. Studies were manually scored by a central masked sleep reading center using American Academy of Sleep Medicine diagnostic criteria. An apnea hypopnea index of 5 or more was considered diagnostic of OSA. Perinatal outcomes were compared between women with and without OSA. RESULTS: Among 175 women, OSA prevalence was 15.4% (13 mild, 9 moderate, 5 severe). Compared with no OSA (apnea hypopnea index less than 5), the OSA group had a higher BMI (46.8+/-12.2 compared with 38.1+/-7.5; P=.002) and more chronic hypertension (55.6% compared with 32.4%, P=.02). Maternal complications included maternal death (n=1, amniotic fluid embolus [no OSA group]) and cardiac arrest (n=1, intra-operative at cesarean delivery [OSA group]). One previable birth and two stillbirths occurred in the no OSA group. Among live births, OSA was associated with more frequent cesarean delivery (65.4% compared with 32.8%; P=.003), preeclampsia (42.3% compared with 16.9%; P=.005), and neonatal intensive care unit admission (46.1% compared with 17.8%; P=.002). After controlling for BMI, maternal age, and diabetes, OSA (odds ratio [OR] 3.55, 95% confidence interval [CI] 1.1-11.3), previous preeclampsia (OR 2.79, 95% CI 1.09-7.19), and hypertension (OR 4.25, 95% CI 1.67-10.77) were associated with development of preeclampsia. CONCLUSION: Obstructive sleep apnea among obese pregnant women is associated with more frequent preeclampsia, neonatal intensive care unit admissions, and cesarean delivery. (Obstet Gynecol 2012; 120: 1085-92) DOI: http://10.1097/AOG.0b013e31826eb9d8