Maternal Leisure-time Physical Activity and Risk of Preterm Birth: A Systematic Review of the Literature

Background: Preterm birth is a leading cause of infant death and regular physical activity may reduce the risk for preterm birth because of its beneficial effects on pregnancy complications such as preeclampsia, excessive weight gain, and gestational diabetes. On average, however, pregnant women report lower levels of physical activity compared with those who are not pregnant. This systematic review examined low, moderate and vigorous leisure-time physical activity (LTPA) during pregnancy and the outcome of preterm birth. Methods: Key words related to preterm birth and physical activity were used to search relevant databases (Medline, Cochrane, CINAHL, Sports Discuss and Scopus). Studies were excluded if they did not measure physical activity as an exposure in pregnant women, did not provide information on gestational age at delivery, and were not published in English. All study designs and sample sizes were considered. Results: The search generated 1472 studies. There were 27 studies included in this review of which 23 received high quality reporting scores. A total of 13 studies reported a significant protective effect of LTPA on the risk of preterm birth. Physical activity of both moderate and vigorous levels was associated with a lower risk of preterm birth in a number of studies, with relative risk estimates ranging from 0.08 to 0.90. Low-intensity activity was also significantly associated with a lower odds of preterm birth, provided the duration of such activity was ≥8hr/day at weeks 23-26 (OR=0.56, 95% CI=0.36, 0.87) or \u3e20min/day during the second trimester (aOR=0.36, 95% CI=0.16, 0.78). Fourteen studies reported null findings, while only two studies detected a significantly higher risk of preterm birth with LTPA during pregnancy. Conclusion: This review of literature up to 2014 provides evidence to support the assertion that healthy pregnant women can engage in low, moderate, and even some vigorous levels of LTPA without risk for preterm bi