A longitudinal study of maternal hemodynamics during normal pregnancy

OBJECTIVE: To investigate the maternal hemodynamic changes that occur during normal pregnancy. METHODS: Serial hemodynamic investigations were performed throughout normal pregnancy by thoracic electrical bioimpedance monitoring in 50 healthy women. Analysis of variance with repeated measurements was used to evaluate the time course of a number of hemodynamic indies. RESULTS: The mean heart rate (+/- standard error SE) increased gradually from 87 +/- 2 beats per minute at 10-18 weeks' gestation to 92 +/- 1 beats per minute at 34-42 weeks' gestation. Mean arterial pressure decreased significantly after 14 weeks' gestation and increased significantly after 29 weeks' gestation. During the third trimester, mean cardiac output and mean stroke volume decreased, and mean systemic vascular resistance increased significantly. The course of cardiac output during the third trimester was not uniform in all women; it increased in nine and decreased in 41 women. A significantly higher mean cardiac output was found in nulliparous women compared with multiparous women (mean difference +/- SE 0.76 +/- 0.33 L/minute). The mean (+/- SE) cardiac output increased significantly from 6 (5.49 +/- 0.16 L/minute) to 12 weeks' postpartum (5.91 +/- 0.19 L/minute). CONCLUSION: Mean cardiac output and mean stroke volume decreased in late pregnancy. A significant difference in mean cardiac output was observed between nulliparous and multiparous women. Cardiac output usually, but not invariably, declined during the third trimester.