Maternal cardiovascular hemodynamic adaptation to pregnancy.

Maternal cardiovascular adaptation to pregnancy involves enormous changes. Cardiac output increases in early pregnancy, initially as a result of an increased heart rate, soon followed by an increased stroke volume. Cardiac output continues to increase until midpregnancy, and remains stable afterward, with a possible small decline in the last weeks of pregnancy. Blood pressure decreases in early pregnancy, reaching a minimum in midpregnancy, then returning to baseline levels at term. Consequently, peripheral vascular resistance is reduced throughout pregnancy. Myocardial contractility seems to be increased during all trimesters of pregnancy, thus gradually provoking the development of a mild ventricular hypertrophy. The increase in preload, which develops in concert with the increment in blood volume, leads to an increase in left atrial diameter, which also begins during early pregnancy. During labor, both cardiac output and blood pressure increase. After delivery, cardiac output initially increases, but begins to decrease within the first hour to reach baseline levels 2 weeks postpartum. Most cardiovascular parameters show their greatest changes within 2 weeks postpartum. Five months postnatally, only a mild residual ventricular hypertrophy persists.