Aerobic exercise during pregnancy influences fetal cardiac autonomic control of heart rate and heart rate variability
Introduction
It is generally accepted that the intrauterine environment influences fetal development and may have implications for the long-term health of the child. Factors that influence fetal development can include maternal nutrition, gestational diabetes, obesity or psychosocial factors [1], [2], [3].These conditions can alter fetal growth and subsequently increase risk in the offspring for obesity [4], type 2 diabetes, cardiovascular disease and disorders of the immune system in later life [5], [6]. While the importance of adequate nutrition during pregnancy is understood, less is known about the potential benefits of maternal exercise on fetal outcomes.
In the non-pregnant state, women who exercise regularly have lower cardiovascular risk and experience a reduction in the incidence of obesity, diabetes, and hypertension as evidenced by a decrease in blood pressure, improved glucose tolerance, lower fat mass, and enhanced autonomic tone [7], [8]. In the pregnant state, regular exercise has multiple, positive maternal effects such as decreased pains/discomforts and depression, shorter labor and delivery, fewer pregnancy complications, and faster recovery after delivery [9], [10], [11], [12], [13], [14]. Earlier studies showed that moderate exercise during pregnancy does not increase risk to the fetus [15], [16], [17], [18]. Consequently, the American Congress of Obstetricians and Gynecologists recommended moderate exercise before, during and after pregnancy. However, the question of whether maternal exercise during pregnancy imparts similar benefits to the fetus is largely unanswered.
Previous studies using ultrasound technology to detect differences in baseline fetal heart rate during maternal exercise showed that fetal heart rate (HR) may increase during or immediately after maternal aerobic exercise. This suggests the fetal cardiovascular system is responsive to maternal exercise [19], [20], [21], [22], [23]. However, little is known about how maternal exercise affects fetal HR even though it is recognized that cardiac autonomic control may be influenced by the intrauterine environment [24]. If the fetus responds to the change in hormonal and metabolic milieu resulting from maternal exercise, continuous exposure throughout pregnancy could have a measurable effect on fetal cardiac autonomic control during development. We hypothesized that maternal exercise during pregnancy would result in lower fetal HR and increased HRV. For precise and non-invasive measures of fetal R-R intervals, we used a dedicated fetal biomagnetometer to record magnetocardiograms (MCG) at 28, 32 and 36 weeks gestational age. Fetal MCG has certain advantages compared to other technologies since the fetal cardiac signal can be detected and separated easily from the maternal MCG. This non-invasive technology is able to measure the fetal QRS complex without distortion or loss of signal, making it a safe, reliable and sensitive tool for monitoring fetal cardiac events and movements [25], [26], [27]. Our aim was to determine if maternal exercise throughout pregnancy would influence fetal cardiac autonomic control as indexed by fetal HR and HRV.
Section snippets
Study population
This prospective, longitudinal non-blinded study was designed to determine the influence of self-reported maternal exercise on fetal cardiac autonomic nervous system development. The study was approved by the Kansas City University of Medicine and Biosciences and University of Kansas Medical Center Institutional Review Boards, following the tenets of the Declaration of Helsinki. Recruitment was limited to low-risk, 20–35 year-old women carrying singleton pregnancies that were up to 28 weeks GA.
Results
All women had uncomplicated pregnancies (29 males, 32 females). Baseline characteristics (mean ± SD) included age (29.0 ± 4.0 years in the exercise group; 29.6 ± 4.0 years in the control group), height (sample means 64.5 in. in both groups), pre-pregnant weight (134.7 ± 14.7 lbs in the exercise group; 150.2 ± 30.0 lb in the control group), and BMI (22.8 ± 2.6 in the exercise group; 25.2 ± 4.6 in the control group). Both groups had similar educational backgrounds, ranging from high school diplomas to graduate
Discussion
We found significantly lower fetal HR and increased fetal HRV during the active fetal state at 36 weeks GA in women who performed moderate aerobic exercise during their pregnancy compared to non-exercising women. Similar to previous reports [40], [41], HRV in both time and frequency domains increases with gestational age. This study demonstrates the utility of fetal MCG as a method that allows surveillance of the developing ANS and as a tool sensitive enough to detect group differences.
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Conclusion
This longitudinal, observational pilot study is unique in that we used non-invasive, fetal MCG to provide evidence that maternal exercise throughout gestation results in significantly lower fetal HR and increased fetal HRV in both time and frequency do These new findings suggest that regular maternal aerobic exercise during a healthy, low-risk pregnancy positively influences the development of fetal cardiac autonomic control. Therefore, a regular exercise program during pregnancy may provide
Conflict of interest
The authors do not have any financial and/or personal relationships with other people or organizations which could inappropriately influence their work. There are no conflicts of interest to report.
Acknowledgements
The authors thank Mihai Popescu, PhD and E. A. Popescu, PhD for their contribution and expertise in designing the MatLab routines for fetal HR and HRV analyses. We acknowledge Lori Blanck, R. EEG/EP T and JoAnn Liermann, RN, PhD, for the assistance in data collection and processing. We are grateful to the women who gave their time to participate in this study. This project was supported by the Hoglund Brain Imaging Center and the Kansas City University of Medicine and Biosciences intramural
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