A randomized comparative trial of the efficacy and safety of exercise during pregnancy: design and methods

Use of an exercise intervention for high-risk and vulnerable populations, such as pregnant women at risk for gestational hypertension or preeclampsia, requires special consideration. A comparative trial testing the effects of two types of physical exercises - stretching (a comparator) and walking (a testing intervention) - for sedentary pregnant women at risk for preeclampsia - is presented in this paper. The study was designed to reduce post-randomization bias and dropout rates from both groups, and closely to monitor safety of subjects. The strengths of the study design and methods include use of a run-in phase; use of a stretching exercise as a comparator; multiple ways to measure daily physical activities and the exercise intervention; and tailored support to remove barriers to exercise for subjects. The intervention consists of 40 min of walking at moderate intensity (i.e., 55-69% of maximum heart rate and rating of perceived exhaustion 12-13) five times a week from 18 weeks gestation until birth. The comparator exercise consists of 40 min of stretching exercise without increasing heart rate to more than 10% of resting heart rate, five times a week from 18 weeks gestation until birth. The primary outcome is the incidence of preeclampsia. Secondary outcomes include the physiologic effects of the intervention and birth outcomes.