Physical activity (PA) during pregnancy decreases the risk of developing hypertensive disorders of pregnancy by 40%, yet the underlying molecular mechanisms are unknown. microRNAs (miRNAs) have shown potential in cardiovascular disease prevention and diagnosis. Circulating levels of miR-21-3p and miR-146b-5p are associated with early pregnancy leisure time PA energy expenditure. However, it is not clear how miRNAs levels change in response to exercise across pregnancy. AIM: To determine the change in circulating levels of miRNAs after a 14-week, moderate-intensity aerobic exercise intervention in pregnant women. METHODS: A subset of 10 pregnant women from the Prenatal Exercise and Cardiovascular Health (PEACH) study were included. Participants were randomized to a supervised aerobic exercise program (n = 5) or a control group (n = 5). At 18 to 21 (baseline) and 34 to 36 (postintervention, PI) weeks of pregnancy, a fasted blood draw and neurovascular assessment were carried out. Muscle sympathetic nerve activity burst incidence (BI), heart rate (HR), systolic, diastolic, and mean arterial blood pressure (SBP, DBP, and MAP, respectively), cardiac output (CO), and plasma miRNA levels were measured at each timepoint. RESULTS: Exercise prevented the rise in BI from baseline to PI. At baseline both miRNA-146b-5p and miR-21-3p levels were not different between groups. miR-21-3p increased from baseline to PI in both groups, but the exercise group had significantly higher levels at PI. CONCLUSION: A 14-week aerobic exercise training intervention during pregnancy increases miR-21-3p levels in maternal plasma. Future work in a larger cohort will allow us to determine the relationship of miR-21-3p with maternal outcomes.

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