Biphasic changes in autonomic nervous activity during pregnancy.

Area of Science:

• Physiology
• Cardiovascular Physiology
• Autonomic Nervous System Function

Background:

• Pregnancy involves significant physiological adaptations, including alterations in the autonomic nervous system (ANS).
• Understanding the sequential changes in ANS activity throughout pregnancy is crucial for monitoring maternal and fetal well-being.

Purpose of the Study:

• To investigate the dynamic changes in heart rate variability (HRV) as a marker of ANS function during the three trimesters of pregnancy.
• To compare ANS activity in pregnant women with non-pregnant controls across different recumbent positions.

Main Methods:

• Heart rate variability (HRV) was assessed in 23 first-trimester, 23 second-trimester, and 21 third-trimester pregnant women, alongside 20 non-pregnant controls.
• Time and frequency domain HRV measures were analyzed in supine and right lateral decubitus positions.
• Statistical comparisons were made between groups and across trimesters.

Main Results:

• Normalized high-frequency power (vagal modulation) was elevated in the first trimester but decreased progressively through the third trimester.
• The low-/high-frequency power ratio (sympathovagal balance) showed an initial decrease in the first trimester, followed by a progressive increase into the third trimester.
• Changes in HRV with postural shifts correlated negatively with supine HRV, indicating altered autonomic regulation.

Conclusions:

• Autonomic nervous activity during pregnancy exhibits a biphasic pattern: higher vagal and lower sympathetic tone in early pregnancy, shifting to lower vagal and higher sympathetic tone in late pregnancy.
• Hemodynamic adaptations and aortocaval compression by the growing uterus likely contribute to these sequential ANS modulations.
• HRV analysis provides valuable insights into the dynamic autonomic adjustments during the course of pregnancy.