Exercise during pregnancy and risk of preterm birth in overweight and obese women: a systematic review and meta-analysis of randomized controlled trials

Introduction. The incidence of overweight and obesity in pregnancy has risen significantly in the last decades. Overweight and obesity have been shown to increase the risk for some adverse obstetric outcomes. Lifestyle interventions, such as diet, physical activity and behavior changes, may reduce these risks by promoting weight loss and/or preventing excessive weight gain. The possible impact of exercise on the risk of preterm birth (PTB) in overweight or obese women is controversial. Therefore, the aim of our study was to evaluate the effect of exercise on the risk of PTB in overweight or obese pregnant women. Material and methods. MEDLINE, EMBASE, Web of Sciences, Scopus, ClinicalTrial.gov, OVID and Cochrane Library were searched from their inception to November 2016. This meta-analysis included only randomized controlled trials (RCTs) of pregnant women assigned or not assigned before 25 weeks to an aerobic exercise regimen. Types of participants included overweight or obese (mean body mass index ≥25 kg/m2) women with singleton pregnancies without any contraindication to physical activity. The summary measures were reported as relative risk (RR) or as mean difference (MD) with 95% confidence intervals (CI). The primary outcome was the incidence of PTB <37 weeks. Results. Nine trials including 1502 overweight or obese singleton gestations were analyzed. Overweight and obese women who were randomized in early pregnancy to aerobic exercise for about 30–60 min three to seven times per week had a lower percentage of PTB <37 weeks (RR 0.62, 95% CI 0.41–0.95) compared with controls. The incidence of gestational age at delivery (MD 0.09 week, 95% CI -0.18 to 0.24) and cesarean delivery (RR 0.93, 95% CI 0.77–1.10) were similar in both groups. Women in the exercise group had a lower incidence of gestational diabetes mellitus (RR 0.61, 95% CI 0.41–0.90) compared with controls. No differences in birthweight (MD 16.91 g, 95% CI -89.33 to 123.19), low birthweight (RR 0.58, 95% CI 0.25–1.34), macrosomia (RR 0.92, 95% CI 0.72–1.18) and stillbirth (RR 2.13, 95% CI 0.22–20.4) between the exercise group and controls were found. Conclusions. Overweight and obese women with singleton pregnancy can be counseled that, compared with being more sedentary, aerobic exercise for about 30–60 min three to seven times per week during pregnancy is associated with a reduction in the incidence of PTB. Aerobic exercise in overweight and obese pregnant women is also associated with a significant prevention of gestational diabetes mellitus, and should therefore be encouraged.