Moderate levels of physical activity were observed to result in small decreases in time to pregnancy regardless of women’s BMI.
The observational prospective cohort study used the internet to recruit and administer questionnaires to 3628 women, age 18 to 40. Participants accepted into the study were required to be in stable relationships with male partners, planning to become pregnant, and not receiving any fertility treatments.
The women were given baseline questionnaires to gather information on their demographics, height, weight, reproductive and medical history, lifestyle, and behavior. Follow-up questionnaires were emailed to participants every two months for 12 months or until the participant became pregnant. Eighty-three percent, or 3,027, completed the study.
One of the things the women were asked at baseline was the average number of hours per week they exercised. In addition, they were asked to report different types of moderate and vigorous activity separately. Activities such as running, fast cycling, aerobics, gymnastics, and swimming were characterized as vigorous. Brisk walking, leisurely cycling, golfing and gardening were considered moderate. Assigning values- total metabolic equivalents (METs)- to the activities, the researchers quantified the amount of moderate and vigorous physical activity each participant engaged in.
The participants were categorized by their exercise exposure and the results were further stratified by BMI to see whether the effect of physical activity on time to pregnancy differs according to body weight.
The researchers found that there was an inverse association between vigorous physical activity and how long it took to become pregnant for normal weight women (BMI under 25). In overweight or obese women (BMI of 25 or above) there was no association between vigorous exercise and a longer time to pregnancy.
Moderate physical activity was associated with improved time to pregnancy across the range of BMI. Women who engaged in 20-39 MET hours per week of physical activity had the shortest times to pregnancy.
ASRM President-Elect, Linda Giudice, MD, PhD, noted, “This study is particularly interesting because its participants were recruited from the general population, not from infertility patients. It points out the benefits of moderate exercise to all women who are planning a pregnancy and suggests that women might reduce their time to pregnancy by modulating their exercise programs.”
The American Society for Reproductive Medicine, founded in 1944, is an organization of 8,000 physicians, researchers, nurses, technicians and other professionals dedicated to advancing knowledge and expertise in reproductive biology. Affiliated societies include the Society for Assisted Reproductive Technology, the Society for Male Reproduction and Urology, the Society for Reproductive Endocrinology and Infertility, the Society of Reproductive Surgeons, and the Society of Reproductive Biologists and Technologists.
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