Continuous Positive Airway Pressure (CPAP) for Sleep Apnea in Pregnancy

Inclusion Criteria 1. Singleton gestation. Twin gestation reduced to singleton, either spontaneously or therapeutically, is not eligible unless the reduction occurred before 14 weeks project gestational age. 2. Gestational age at randomization between 14 weeks 0 days and 21 weeks 6 days based on clinical information and evaluation of the earliest ultrasound. 3. Diagnosis with mild to moderate OSA as defined by an AHI score ≥ 5 and \<30. Exclusion Criteria 1. Previously prescribed, current or planned therapy for sleep apnea. 2. Age \< 18 years, because the rate of sleep apnea in this population is extremely low. 3. Inability to sleep in a stable place with access to the CPAP machine at least 5 nights per week. 4. Asthma requiring systemic steroid therapy for more than 14 days within the past 6 months because this population is expected to be unresponsive to CPAP therapy. 5. Current use of prescribed sleeping pills for insomnia. 6. Chronic medical conditions requiring oxygen supplementation (e.g. pulmonary fibrosis, pulmonary hypertension, cystic fibrosis) because this population is expected to be unresponsive to CPAP therapy. 7. Chronic renal disease with serum creatinine \>1.3 mg/dL because the primary outcome would be pre-determined. 8. Antiphospholipid antibody syndrome, because it would compromise the primary outcome diagnosis. 9. History of medical complications such as: 1. Active liver disease (acute hepatitis, chronic active hepatitis, persistently abnormal liver enzymes) 2. Thrombocytopenia with platelet count \<100,000 because of the difficulty in assessing the primary outcome. 10. Active vaginal bleeding (more than spotting) at the time of randomization. 11. Known chromosomal, genetic, major malformations or fetal demise, or planned termination of pregnancy because inclusion would compromise evaluation of secondary neonatal outcomes. 12. Known major uterine malformations associated with adverse pregnancy outcomes. 13. Current use of opiates (heroin, methadone, or other daily opioid use) due to inaccuracy of the home sleep test and inefficiency of CPAP. 14. Active drug use, alcohol use, or unstable psychiatric condition. 15. Participation in another interventional study that influences preeclampsia, hypertensive disorders of pregnancy, or GDM. 16. Prenatal care or delivery planned at a non-network center where access to the complete electronic medical record will not be available to research staff. 17. Participation in this trial in a previous pregnancy. Patients who were screened in a previous pregnancy, but not randomized, may be included.