Effects of Exercise During Pregnancy on Maternal Heart Rate and Heart Rate Variability

Background: Pregnancy is associated with an increased sympathetic state, which can be exacerbated by gestational conditions. Research has shown that exercise during pregnancy lowers heart rate (HR) and can attenuate the symptoms of gestational conditions associated with increased sympathetic control. However, changes in maternal heart autonomic function in response to exercise have not been reported across multiple time points during pregnancy. This analysis is designed to address this gap. Objective: To determine if exercise throughout gestation improves maternal cardiac autonomic nervous system functioning, as evidenced by decreased HR and increased heart rate variability (HRV) indices. Design: Case control study. Setting: Academic medical institution. Participants: A total of 56 women with healthy, singleton, low-risk pregnancies. Methods: Participants were asked to complete 3 resting 18-minute HRV recordings at 28, 32, and 36 weeks' gestation, along with a physical activity questionnaire. Main Outcome Measures: HRV indices were calculated for time (R peak to R peak interval standard deviation and root mean squared of successive differences) and frequency (very low, low, and high frequency) domain measures. The differences between groups were compared for HRV indices at 28, 32, and 36 weeks. Results: Resting HR was significantly lower in the exercise group at 28 weeks (P < .01) compared with the control group. The exercise group had significantly (P < .05) increased measures of resting HRV time domain measures at 28, 32, and 36 weeks' gestation compared with the control group. Resting HRV power was significantly increased (P < .05) in all frequency domain measures at 32 weeks in the exercise group relative to the control group. No differences occurred in sympathovagal balance (low frequency/high frequency ratio) between groups. Conclusion: Exercise throughout pregnancy can significantly improve cardiac autonomic control. More research is needed to determine if this adaptation to exercise may reduce the risk of adverse outcomes associated with gestational conditions with poor autonomic control, such as diabetes, hypertension, pre-eclampsia, and excessive weight gain.