Serial noninvasive evaluation of cardiovascular hemodynamics during pregnancy.

M-mode echocardiography, in combination with electrocardiography and phonocardiography, has been used to measure pulmonary capillary pressure as well as other cardiac functions. Serial hemodynamic evaluations by use of this technique were performed in seven healthy pregnant women in the recumbent position. Each patient had five studies: four antenatal studies and one postpartum study that served as a control. Mean pulmonary capillary pressure was within normal limits throughout pregnancy and the puerperium. Cardiac output did not increase significantly by the end of the first or second trimester but became elevated by 31% in the early third trimester. This elevation in cardiac output persisted until delivery and resulted from a comparable increase in heart rate. Stroke volume and ejection fraction did not change significantly, while peripheral vascular resistance fell, although not significantly, reaching a nadir at approximately 28 weeks of gestation. Our findings indicate that maternal cardiac output increases due to an increased heart rate and reduced afterload.