OBJECTIVE: To evaluate the association between physical exercise during pregnancy and maternal gestational weight gain and fetal cardiac function. METHODS: This was a randomized controlled trial of women with a singleton pregnancy managed from the first trimester at the Hospital de Torrejon, Madrid, between November 2014 and June 2015. Women were randomized to either follow a supervised physical conditioning program, consisting of a 60-min session 3 days per week for the duration of pregnancy, or not attend any exercise program (controls). The primary outcome was maternal weight gain during pregnancy. Secondary outcomes included fetal cardiac function parameters evaluated at 20, 28 and 36 weeks' gestation, Cesarean section, preterm delivery, induction of labor and birth weight. A sample size of 45 in each group was planned to detect differences in maternal weight gain of at least 1 kg, with a power of > 80% and alpha of 0.05. RESULTS: During the study period, 120 women were randomized into the exercise (n = 75) and control (n = 45) groups. Following exclusions, the final cohort consisted of 42 women in the exercise group and 43 in the control group. Baseline characteristics (maternal age, prepregnancy body mass index, parity, conception by in-vitro fertilization, Caucasian ethnicity, physical exercise prior to pregnancy and smoker) were similar between the two groups. No differences were found between the groups in maternal weight at 20, 28, 36 and 38 weeks' gestation or in weight gain at 38 weeks. However, the proportion of women with weight loss >= 9 kg at 6 weeks postpartum was higher in the exercise compared with the control group (68.2% versus 42.8%; relative risk 1.593; p = 0.02). The ductus arteriosus pulsatility index (DA-PI) at 20 weeks (2.43 +/- 0.40 versus 2.26 +/- 0.33, p < 0.05) and the ejection fraction (EF) at 36 weeks (0.85 +/- 0.13 versus 0.81 +/- 0.11, p < 0.05) were higher in the exercise compared with the control group. All other evaluated fetal cardiac function parameters were similar between the two groups. CONCLUSIONS: Performing exercise during pregnancy is not associated with a reduction in maternal weight gain but increases weight loss at 6 weeks postpartum. Physical exercise during pregnancy is associated with increased fetal DA-PI at 20 weeks and EF at 36 weeks, which could reflect adaptive mechanisms.

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