Maternal cardiovascular dynamics: IV. The influence of gestational age on the maternal cardiovascular response to posture and exercise

Abstract

Serial hemodynamic evaluations were carried out in 11 patients during pregnancy and the postpartum period. The patients were studied at rest in the supine, lateral, and sitting positions as well as during and after exercise on a bicycle ergometer. The cardiac output was found to be elevated to peak levels as early as 20 to 24 weeks of gestation and was maintained at this high level through the thirty-second week of gestation. At 38 to 40 weeks there was a decline in cardiac output in all positions. This fall was most pronounced in the supine position, in which the cardiac output was found to be lower than in the same position during the postpartum period. The heart rate increased only slightly during early gestation but continued to rise throughout pregnancy in the supine and lateral positions. Accordingly, The stroke volume showed a progressive decline from 20 to 24 weeks of gestation to term. The cardiovascular response to mild exercise was constant throughout pregnancy and similar to that encountered in nonpregnant individuals. However, moderate exercise indicated there is a progressive decline in circulatory reserve as pregnancy advances. This is not attributed to any change in cardiac function but rather to peripheral pooling of blood and obstruction to venous return by the large gravid uterus. Following exercise cardiovascular function returned to resting levels with equal rapidity during pregnancy and post partum.