Hemodynamic changes during twin pregnancy. A Doppler and M-mode echocardiographic study.

Serial hemodynamic investigations were performed in 10 women with twin pregnancies at 20, 24, 28, 32, and 36 weeks' gestation and at 6 months after delivery. Cardiac output was measured by Doppler and cross-sectional echocardiography at the aortic, pulmonary, and mitral valves. Cardiac chamber size and ventricular function were investigated by M-mode echocardiography. The hemodynamic results were compared with those of 13 women with singleton pregnancies. Mean Doppler cardiac output was increased at 20 weeks of twin pregnancy (7.63 L/min) and showed no significant change during the remainder of pregnancy, but fell to 5.07 L/min after delivery. This increase was significantly greater than that recorded during singleton pregnancy, because of a relatively greater increase in heart rate. Twin pregnancy was associated with a significantly greater increase in left atrial dimension, but the increases in left ventricular dimensions, wall thickness, and function were comparable to those recorded in singleton pregnancy.