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Background: Preeclampsia is a leading cause of maternal morbidity and perinatal mortality. Manifestations include hypertension, proteinuria, and end-organ dysfunction in the latter half of pregnancy. The United States Preventive Services Task Force recommends low-dose aspirin as a modestly effective preventive treatment; however, no conclusive prevention is currently available. Moderate to vigorous physical activity is reported to reduce preeclampsia risk, but is increasingly difficult by the 3rd trimester. Further, intense exercise may stimulate sympathetic overactivation, a precursor of late-onset (≥34 weeks gestation) preeclampsia associated with maternal obesity. Stretching exercise may be a feasible alternative to intense exercise, and more readily adopted by obese women at risk of late-onset preeclampsia. We hypothesized that stretching exercise would suppress sympathetic overactivity and enhance parasympathetic tone in pregnant women.Methods: Gravid women were recruited with informed consent for stretching exercise and cardiovascular testing during the 2nd to 3rd trimester of pregnancy. Exercises were standardized by video demonstration, and targeted 14 major muscle groups in the lower and upper extremities. Each muscle group was stretched for 20 seconds in 3 repetitions. Blood pressure, carotid-femoral pulse wave velocity (PWV), and heart rate variability (HRV) were acquired before and after stretching, with baseline values preceded by a 15 minute rest. Heart rate and HRV were averaged over 10 minute acquisitions. Total HRV variance was stratified into low frequency (LF; < 0.15 Hz) and high frequency (HF; ≥ 0 .15 Hz) domains, with HF reflecting parasympathetic nerve activity and LF dominated by sympathetic activity. Sympathovagal balance was estimated by the LF/HF ratio. Pre- and post-exercise measurements were compared by paired t-tests.Results: A total of 20 women consented to enrollment; all completed stretching exercise and cardiovascular testing without complications. On average, study participants were 32 years old, 27 weeks pregnant, and had a BMI of 29 kg/m2. Over a third (35%) had a BMI > 30 kg/m2. Significant reductions between pre- and post-exercise were observed for mean diastolic blood pressure (60 vs. 57 mmHg; p=0.02) and heart rate (78 vs. 75 bpm; p<0.0001). However, mean systolic blood pressure was not significantly changed (104 vs. 105 mmHg; p=0.2), nor was mean PWV (5.3 vs. 5.2 m/s; p=0.4). Although non-significant, the mean LF/HF ratio decreased (2.4 vs. 1.7 Hz; p=0.3), suggesting parasympathetic dominance post-exercise.Conclusion: This pilot study demonstrates stretching exercise is well-tolerated by pregnant women in the 2nd or 3rd trimester, and may be a feasible prevention for obese women at risk of late-onset preeclampsia. A randomized controlled trial investigating outcomes of routine stretching exercise in pregnancy is warranted.