Cardiac output in normal pregnancy measured by impedance cardiography.

Impedance cardiography was used to study cardiodynamic changes throughout normal pregnancy. Stroke volume, heart rate and cardiac output were determined in fourteen normal primigravidae from early pregnancy until 6-25 weeks after delivery. To elucidate the influence of the patient's position on cardiac output, measurements were made in the supine as well as in the left and right lateral positions. Stroke volume and cardiac output increased up to the 28th week of pregnancy and then decreased during late pregnancy. These changes seemed to be independent of the patient's position. After delivery a further reduction in cardiac output due to a significant decrease in heart rate was found. No significant differences in cardiac output were found between right and left lateral position. However, during pregnancy as well as after delivery, cardiac output measured by impedance cardiography was significantly higher in the supine position than in the lateral positions. Thus, the impedance method does not seem to be reliable in measuring absolute values of stroke volume and cardiac output but may be used for relative measurements during pregnancy.