Normal pregnancy and oxygenation during sleep.

Pregnancy is associated with significant alterations in respiratory function. Changes during pregnancy include reduced functional residual capacity (FRC) and residual volume (RV), increased alveolar-arterial difference for oxygen (A-alphaPO2) and in the supine position, reduced cardiac output. In conjunction with sleep-related apneas or hypopneas, these could lead to maternal oxygen desaturation during sleep. Because of the conflicting data from sleep studies in late pregnancy, we performed complete polysomnography on 11 pregnant women at 36 weeks of gestation and again postpartum. We also measured the PaO2, every 2h. The frequency of apneas and hypopneas was significantly lower during pregnancy compared with that on the postpartum control night. PaO2 levels in the supine position, during sleep, were also significantly lower during pregnancy compared to the postpartum period. No correlation was observed between PaO2 levels and apneas or hypopneas or percent of REM sleep.