Maternal Cardiovascular Responses to Position Change in Pregnancy

SIMPLE SUMMARY: Pregnancy requires major adaptions to blood circulation in the mother, because the developing baby needs an increasing supply of nutrients from the mother to grow. We know that this blood circulation can be influenced by position, for example, when the mother sits, stands or lies on her back. Some positions, like lying on the back, can increase risk of pregnancy loss. We present research that provides evidence for how blood supply is changed by both pregnancy and position. The primary aim of this work is to provide a description of what is expected in a normal pregnancy, so that we can provide a basis for future studies that investigate pregnancies that are not going as well as they should. ABSTRACT: The maternal cardiovascular-circulatory system undergoes profound changes almost from the conception of a pregnancy until the postpartum period to support the maternal adaptions required for pregnancy and lactation. Maintenance of cardiovascular homeostasis requires changes in the cardiovascular autonomic responses. Here, we present a longitudinal study of the maternal cardiovascular autonomic responses to pregnancy and maternal position. Over a normal gestation, in the left lateral position there are significant changes in both time and frequency domain parameters reflecting heart rate variability. We show that cardiovascular autonomic responses to physiological stressors (standing and supine positions in late pregnancy) became significantly different with advancing gestation. In the third trimester, 60% of the subjects had an unstable heart rate response on standing, and these subjects had a significantly reduced sample entropy evident in their heart rate variability data. By 6 weeks, postpartum function returned to near the non-pregnant state, but there were consistent differences in high-frequency power when compared to nulligravid cases. Finally, we review complementary evidence, in particular from magnetic resonance imaging, that provides insights into the maternal and fetal impacts of positioning in pregnancy. This demonstrates a clear relationship between supine position and maternal hemodynamic parameters, which relates to compression of the inferior vena cava (p = 0.05). Together, these studies demonstrate new understanding of the physiology of physiological stressors related to position.