A 32 yr-old woman in her last trimester of pregnancy was found to have severe obstructive sleep apnea (OSA). The overnight polysomnogram demonstrated an apnea plus hypopnea index of 159 events per hour. Apneas were associated with severe oxygen desaturation to 40% during rapid eye movement sleep, maternal bradycardia, and second degree heart block. External cardiotocography showed normal fetal heart rate reactivity to fetal movements, even during the apneas and episodes of oxygen desaturation. Nasal continuous positive airway pressure at a level of 15 cm H2O effectively treated the apneas and desaturation and had no effect on the fetal heart rate. The patient was induced electively during the 39th wk of pregnancy and gave birth to a newborn with growth retardation. Early recognition and treatment of OSA in pregnancy might prevent problems with fetal development.