Haemodynamic changes in the second half of pregnancy: a longitudinal, noninvasive study with thoracic electrical bioimpedance

Abstract

Objective: Maternal cardiovascular adaptations to pregnancy are necessary for an adequate fetomaternal circulation. However, the time course of physiological haemodynamic changes during the second half of pregnancy remains unclear. Various methods, invasive and noninvasive, are described to measure these changes. The thoracic electrical bioimpedance (TEB) technique is a method which is especially suitable to measure haemodynamic changes over time. The aim of the study was to determine both individual and group trends of haemodynamic changes in healthy pregnant women during the second half of pregnancy by means of TEB. Outcome variables are heart rate (HR), stroke volume (SV), cardiac output (CO) and blood pressure.

Design: Longitudinal study.

Setting: Outpatient antenatal care clinic of university hospital.

Population: A total of 22 healthy nonsmoking women with an uncomplicated singleton pregnancy and without pre-existing vascular disorders were invited.

Methods: TEB and blood pressure measurements were performed at each regular visit from about 24 weeks of gestation through term age.

Main outcome measures: Trends were calculated with the random effects model.

Results: Data obtained from 19 women were analysed, with a median of eight (range 3-11) measurements. HR showed a linear increase (P < 0.0005) and a quadratic trend (P < 0.0005). SV decreased linearly (P = 0.046), without a quadratic course. CO remained stable over time.

Conclusion: During the second half of physiological pregnancy, significant trends could be determined. An increase in HR, a decrease in SV, a stable CO and an increase in systolic and diastolic blood pressures were found.