Low-Intensity Exercise and Pregnancy Outcomes: An Examination in the Nurses' Health Study II

Background: The benefit of low-intensity exercise (LIE) during pregnancy is poorly understood at a time when few women participate in moderate or vigorous exercise. Using data from the Nurses' Health Study II (NHSII), we tested the hypothesis that women who engaged in more LIE before and during pregnancy experience fewer pregnancy complications. Methods: Among 116,429 U.S. female registered nurses (25-42 years of age) who were enrolled in NHSII in 1989, we included participants (36-50 years of age) who reported in 2001 or 2005 that they were pregnant and completed questionnaires about pregnancy "low-intensity exercise (yoga, stretching, toning)," and who in 2009, provided a full pregnancy outcome history. Multivariable-adjusted relative risk (RR) and 95% confidence intervals (CIs) were calculated between LIE and adverse pregnancy outcomes using log-binomial regression models. Results: Among 225 eligible pregnant participants, 71 (31.6%) reported engaging in any LIE. LIE was associated with lower preterm birth, but not significantly associated with pregnancy loss or other adverse pregnancy outcomes. The RR for any LIE for preterm birth was 0.31 (95% CI: 0.09-1.07), with a significant dose-response association [RR = 0.65 (95% CI: 0.48-0.89) per every 30-minute session]. Some suggestive inverse associations were also observed for other adverse pregnancy outcomes: the RR for any LIE for low birthweight was 0.35 (95% CI: 0.08-1.48); for preeclampsia/gestational hypertension was 0.51 (95% CI: 0.13-1.96); and for gestational diabetes was 0.64 (95% CI: 0.25-1.64). Conclusion: Pregnant women can include yoga, stretching, and toning exercise for promoting wellbeing.