Effect of physical activity on gestational age and preterm birth: The HUNT study

Background The level of physical activity (PA) in the general population is considered too low, and this has also been shown for pregnant women. Although recent research has shown that regular moderate PA may be beneficial both for the mother and the fetus in relation to complications during pregnancy, the effect of being physically active before and during pregnancy is still debated. Objectives The aim of this study is to examine the effect of PA before and during pregnancy in relation to mean gestational age and risk of preterm birth in a large cohort of women. Subjects The study included a total of 2,515 women in HUNT 1 and 2,921 women in HUNT 2 aged between 20 and 35 years at the time of participation, and who had given birth during the following 5 years after the HUNT study. Methods Gestational age obtained from The Medical Birth Registry of Norway. In HUNT 1, PA was reported as frequency, intensity and duration, and in HUNT 2, hours of light and hard PA per week was reported. For both studies a summary score combining information from the separate items was constructed, classifying participants into the following groups: No, light, medium, or high activity. Using linear regression to calculate adjusted mean differences in gestational length between the activity groups, and logistic regression to calculate adjusted odds ratios (ORs) as estimates of relative risk of preterm birth (gestational age