Prenatal exercise reduces the serious complications of pregnancy (eg, gestational diabetes, preeclampsia, hypertension) without increasing the risk of having a miscarriage, preterm delivery or low birth weight baby. While pregnant women are encouraged to exercise, the impact of prenatal exercise on cardiorespiratory fitness has not been synthesised. The aim of this systematic review was to assess the effects of prenatal exercise on maternal cardiorespiratory fitness and health compared to not exercising.

Sensitive searches of eight databases were used to locate randomised controlled trials involving pregnant women (at any stage of pregnancy) undertaking an exercise program that started post-conception and lasted for at least 1 week compared to no exercise intervention. The main outcomes were cardiorespiratory fitness (maximal aerobic capacity, submaximal aerobic capacity, aerobic capacity at anaerobic threshold) and cardiorespiratory health (resting heart rate and blood pressure). Two independent reviewers selected trials and extracted the data. Trial quality was evaluated with the Cochrane risk of bias tool and the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) tool was used to determine the certainty of the evidence. Meta-analyses were performed for each outcome and are reported as mean difference (95% confidence interval). Five subgroup analyses were prespecified: (1) with vs. without diabetes; (2) pre-pregnancy body mass index >=25 kg/m2 vs. <25 kg/m2; (3) previously inactive vs. previously active; (4) exercise dose and timing; and, (5) type of test for cardiorespiratory fitness.

26 trials (2,292 participants) were included in the review. Exercise was 2-7 days/week, for 15-60 minutes/session, and started 6-32 weeks into the pregnancy. Exercise modalities included walking, stationary cycling, strength training, aerobics and combined exercises.

There was high certainty evidence that exercise increased absolute maximum aerobic capacity (0.25 L/min (0.11 to 0.39), 3 trials, 77 participants) and relative submaximal aerobic capacity (0.61 mL/kg/min (0.17 to 1.04), 3 trials, 177 participants) compared to not exercising. There was low certainty evidence that exercise increased relative maximal aerobic capacity (2.77 mL/kg/min (0.32 to 5.21), 5 trials, 430 participants) but did not change aerobic capacity at the anaerobic threshold (1.22 mL/kg/min (-0.83 to 3.28), 2 trials, 116 participants). There was high certainty evidence that exercise reduced resting heart rate (-1.7 bpm (-3.2 to -0.2), 9 trials, 637 participants) and low quality evidence that exercise decreased resting systolic blood pressure (-2.1 mmHg (-3.7 to -0.5), 16 trials, 1,672 participants) and resting diastolic blood pressure (-1.8 mmHg (-2.9 to -0.6), 15 trials, 1,624 participants) compared to not exercising.

The subgroup analyses indicated that trials with an exercise duration of <20 weeks had greater reductions in resting diastolic blood pressure than those lasting >20 weeks (-2.9 vs. -0.9 mmHg) and trials that initiated exercise <16 weeks gestational age had smaller reductions in resting diastolic blood pressure than those starting at 16-20 weeks or >20 weeks (-0.9 vs. -2.8 vs. -3.9 mmHg). The other subgroup analyses were inconclusive due to the low number of studies analysed in each category.

Exercise interventions initiated after conception improve maternal cardiorespiratory fitness and health.

Cai C, et al. Prenatal exercise and cardiorespiratory health and fitness: a meta-analysis. Med Sci Sports Exerc 2020 Jan 17:Epub ahead of print

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