Acute Fetal Response to High-Intensity Interval Training in the Second and Third Trimesters of Pregnancy

The majority of women do not meet the recommended levels of exercise during their pregnancies, frequently due to a lack of time. High-intensity interval training offers a potential solution, providing an effective, time-efficient exercise modality. This exercise modality has not been studied in pregnancy therefore, the objective of this study was to evaluate fetal response to a high-intensity interval training resistance circuit in the late second and early third trimesters of pregnancy. Fourteen active, healthy women with uncomplicated, singleton pregnancies participated in a high-intensity interval training resistance circuit between 28+0/7 and 32+0/7 weeks. A Borg rating of perceived exertion of 15-17/20 and an estimated heart rate of 80-90% of maternal heart-rate maximum was targeted. Fetal well-being was evaluated continuously with fetal heart-rate tracings and umbilical artery Doppler velocimetry conducted pre-and post-exercise. Fetal heart rate tracings were normal throughout the exercise circuit. Post-exercise, umbilical artery end-diastolic flow was normal and significant decreases were observed in the mean systolic/diastolic ratios, pulsatility indexes and resistance indexes. Therefore, in a small cohort of active pregnant women, a high-intensity interval training resistance circuit in the late second and early third trimesters of pregnancy appears to be a safe exercise modality with no acute, adverse fetal effects but further study is required. Novelty: • High-Intensity Interval Training, at an intensity in excess of current recommendations, does not appear to be associated with any adverse fetal effects in previously active pregnant women. • High-Intensity Interval Training is an enjoyable and effective exercise modality in previously active pregnant women.