American Journal of Epidemiology Advance Access originally published online on February 25, 2008
American Journal of Epidemiology 2008 167(7):859-866; doi:10.1093/aje/kwm364
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ORIGINAL CONTRIBUTIONS |
Physical Exercise during Pregnancy and the Risk of Preterm Birth: A Study within the Danish National Birth Cohort
1 National Institute of Public Health, Copenhagen, Denmark
2 Department of Biostatistics, Institute of Public Health, University of Copenhagen, Copenhagen, Denmark
3 Department of Epidemiology, School of Public Health, University of California, Los Angeles, Los Angeles, CA
4 Department of Epidemiology, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark
5 Department of Epidemiology, Institute of Public Health, University of Aarhus, Aarhus, Denmark
Correspondence to Mette Juhl, National Institute of Public Health, Oster Farimagsgade 5A, 2nd floor, 1399 Copenhagen K, Denmark (e-mail: mju{at}niph.dk).
Received for publication July 20, 2007. Accepted for publication November 13, 2007.
According to many national recommendations, women should be physically active during pregnancy, but empirical evidence to support this recommendation is sparse. The authors' aim in this study was to examine the relation between physical exercise during pregnancy and the risk of preterm birth. Self-reported data on physical exercise during pregnancy were collected prospectively for 87,232 singleton pregnancies included in the Danish National Birth Cohort between 1996 and 2002. Hazard ratios for preterm birth according to hours of exercise per week, type of exercise, and metabolic equivalent-hours per week, respectively, were calculated using Cox regression analysis. Results showed a reduced risk of preterm birth among the almost 40% of women who engaged in some kind of exercise during pregnancy in comparison with nonexercisers (hazard ratio = 0.82, 95% confidence interval: 0.76, 0.88), but no dose-response relation was seen. The association was not affected by the type of exercise, and the results were not altered when the degree of preterm birth was taken into account. These findings do not indicate any adverse effects of exercise on the risk of preterm birth and therefore do not contradict current recommendations.
exercise; pregnancy; premature birth
Abbreviations: CI, confidence interval; MET, metabolic equivalent