Washington, DC -- While it may seem counterintuitive, women who regularly exercised for four or more hours per week in the previous nine years or less were 40% less likely to have a live birth after their first cycle of in vitro fertilization (IVF) than women who didn't exercise, according to a new study published in the October issue of Obstetrics & Gynecology. Regular exercisers were also twice as likely to have an implantation failure or pregnancy loss after undergoing IVF than women who did not exercise. Cardiovascular exercise, in particular, was associated with a 30% lower likelihood of successful live birth compared with nonexercisers.

The health benefits of exercise are well known, but the effect of exercise on fertility is more complex. Infertility and anovulation (no ovulation) are common among female athletes who train intensively, as well as among women with low body mass indexes. Evidence shows that being overweight or obese is linked to infertility as well. What is not known is how exercise may affect the success rate of IVF treatments.

With a grant from the National Institutes of Health, researchers analyzed prospective data on 2,232 women who underwent IVF treatments at one of three clinics in the Boston area from 1994 to 2003. Of these women, 61.3% reported that they exercised regularly, and 38.5% reported that they didn't exercise. Women exercisers were broken down into three different groups based on their primary type of exercise: walking, cardiovascular (eg, jogging, aerobics, treadmill), and other (eg, swimming, yoga, team sports). These three groups were further broken down into four basic categories based on the number of hours per week and the number of years that they had been exercising.

The study found that, in general, women who reported walking for exercise had essentially the same likelihood of successful live births after their first IVF treatment when compared to nonexercisers. However, the subgroup of women who walked for four or more hours per week for the previous nine years or less were 50% less likely to have a successful live birth after IVF compared with nonexercisers.

Women who engaged in cardiovascular exercise for four or more hours per week over the previous nine years or less had a 50% reduction in live births compared with nonexercisers. Women who did cardiovascular exercise fewer hours per week for 10 years or longer also experienced a lesser likelihood of successful birth, but it was a weaker effect compared with the cardiovascular group who exercised greater than four hours per week for nine years or less.

The researchers found that exercise in general seems to be associated with a reduced success rate after the first cycle of IVF, with cardiovascular exercise more detrimental than walking. Women who exercised the most in the previous nine years seemed to be most affected. The researchers theorize that exercise affects hormones as well as body mass index, but say that more study is needed to clarify the relation between exercise and the success of IVF.

Contact: Mark D. Hornstein, MD, Brigham and Women's Hospital, Boston, MA, at mhornstein@partners.org

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