Is Moderate Intensity Exercise during Pregnancy Safe for the Fetus? An Open Clinical Trial

Abstract Objective To determine the effect of treadmill walking on maternal heart rate (MHR) and cardiotocographic parameters (basal fetal heart rate [FHR], active fetal movements [AFM], number of accelerations and decelerations, and short-term variation [STV] and long-term variation [LTV] of fetal heart rate) in pregnant women at 36 weeks. Methods A nonrandomized, open clinical trial involving 88 healthy pregnant women submitted to moderate intensity walking and computed cardiotocography in 3 20- minute periods (resting, treadmill walking, and postexercise recovery). Results The mean FHR decreased during walking (resting: 137 bpm; treadmill: 98 bpm; recovery: 140 bpm; p<0.001), with bradycardia occurring in 56% of the fetuses in the first 10minutes of exercise, and in 47% after 20minutes. Bradycardia was not detected in the other phases. The mean STV and HV were 7.9, 17.0, and 8.0 milliseconds (p<0.001) and 7.6, 10.8 and 7.6 bpm (p=0.002) in the resting, walking and recovery phases, respectively. Themean number of fetalmovements in 1 hour was 29.9, 22.2 and 45.5, respectively, in the 3 periods (p<0.001). In overweight/obese women, the mean FHR was lower (p=0.02). Following the logistic regression analysis, two variables remained significantly associated with bradycardia: maternal fitness in the 28th week of pregnancy (protective effect) and maternal weight (increased risk). Conclusion In healthy fetuses, physical exercise proved to be safe, since, although FHR and AFM decreased during treadmill walking, an increase in SVT and LTV was observed.