BACKGROUND: Fetal growth is dependent upon utero-placental vascular supply of oxygen and nutrients from the mother and has been proposed to be compromised by vigorous intensity exercise in the third trimester. The aim of this systematic review was to investigate the effects of vigorous intensity exercise performed throughout pregnancy, on infant and maternal outcomes. METHODS: Electronic searching of the PubMed, Medline, Embase, Cochrane Library, Web of Science and CINAHL databases was used to conduct the search up to November 2018. Study designs included in the systematic review were randomised control trials, quasi-experimental studies, cohort studies and case-control studies. The studies were required to include an intervention or report of pregnant women performing vigorous exercise during gestation, with a comparator group of either lower intensity exercise or standard care. RESULTS: Ten cohort studies (n = 32,080) and five randomized control trials (n = 623) were included in the systematic review (n = 15), with 13 studies included in the meta-analysis. No significant difference existed in birthweight for infants of mothers who engaged in vigorous physical activity and those who lacked this exposure (mean difference 8.06 g, n = 8,006). Moreover, no significant increase existed in risk of small for gestational age (risk ratio 0.15, n = 4,504), risk of low birth weight (< 2,500 g) (risk ratio 0.44, n = 2,454) or maternal weight gain (mean difference -0.46 kg, n = 1,834). Women who engaged in vigorous physical activity had a small but significant increase in length of gestational age before delivery (mean difference 0.21 weeks, n = 4,281) and a small but significantly reduced risk of prematurity (risk ratio -0.20, n = 3,025). CONCLUSIONS: Findings from this meta-analysis indicate that vigorous intensity exercise completed into the third trimester appears to be safe for most healthy pregnancies. Further research is needed on the effects of vigorous intensity exercise in the first and second trimester, and of exercise intensity exceeding 90% of maximum heart rate. TRIAL REGISTRATION: PROSPERO trial registration CRD42018102109.

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