Pattern of Cardiac Autonomic Modulation Assessed by Heart Rate Variability in Normal Pregnancy: A Longitudinal Cohort Study

Introduction: Normal pregnancy is associated with adaptive maternal haemodynamics, viz., increase in blood volume, Heart Rate (HR), cardiac output, and fall in blood pressure. Alterations in hormones and plausible autonomic modulation may regulate these haemodynamic changes and failure of such alterations could have clinical consequences like pregnancy-induced hypertension and preeclampsia. Heart Rate Variability (HRV), a non-invasive measure of cardiac autonomic activity may provide insights in pattern of cardiac autonomic modulation during pregnancy, and tracking it may be useful clinically. Aim: To evaluate the pattern of cardiac autonomic modulation assessed by HRV during the course of healthy pregnancy. Materials and Methods: The present longitudinal cohort study was conducted from August 2019 to April 2021 in SKNMC & GH, Pune, Maharashtra, India. A total of 31 pregnant females who underwent repeated HRV assessment between 11th-13th, 18th to 20th, and 24th to 26th weeks of gestation and tracked for pregnancy outcome till delivery, were included. High sampled Electrocardiogram (ECG) (1Kz) for 15 minutes was recorded in supine left lateral position and HRV indices from last five minutes were measured. Multiple group comparisons and between-group comparisons were done using non parametric tests and p<0.05 was considered significant. Results: The mean age of 31 pregnant females was 24.1±3.4 years. Significant increase in average HR (p=0.002)was observed from first to third trimester significant decrease in overall HRV (p=0.01), total power (ms2 ) (p=0.008), High Frequency (HF) (ms2 ) (p=0.03) and Low Frequency (LH) (ms2 ) (p=0.001) was also observed. A trend in HFnu decrement was observed. Conclusion: As pregnancy advances, (till 26 weeks) a pattern of parasympathetic withdrawal (decreased overall variability and HF (ms2 ) along with increase in average HR and reduced baroreflex sensitivity (decrease in LF power) was observed with healthy pregnancy.