Physiologic changes during normal pregnancy and delivery.

The major adaptations of the maternal cardiovascular system that progress throughout gestation may unmask previously unrecognized heart disease and result in significant morbidity and mortality. Most of these changes are almost fully reversed in the weeks and months after delivery. Hemodynamic changes during pregnancy include increased blood volume, cardiac output (CO), and maternal heart rate; decreased arterial blood pressure; decreased systemic vascular resistance. CO increases up to 30% in the first stage of labor, primarily because of increased stroke volume; maternal pushing efforts in the second stage of labor can increase CO by as much as 50%.