Fitness and fertility
Being in great physical shape doesn't guarantee pregnancy, and it may even reduce the odds for certain women using in vitro fertilization treatments.
Research published today in the October issue of Obstetrics & Gynecology found that women who exercised four or more hours per week–and had done so for the previous one to nine years–were 40 percent less likely to have a baby after their first IVF treatment than if they hadn't exercised. Surprisingly, however, women who had followed a rigorous fitness regimen for 10 to 30 years were just as likely to end up with a baby as women who didn't exercise.
Excessive exercise can stress a woman's reproductive system, causing her body to "protect" it from a pregnancy it's not prepared to maintain–perhaps by causing subtle hormonal changes, theorizes Mark Hornstein, senior researcher and clinical director of reproductive endocrinology at Brigham and Women's Hospital in Boston. Why does the effect seem to wear off after 10 years? "We don't have a good answer for that," says Hornstein. "It may be that the body accommodates."
A closer look at the data showed that intense cardiovascular exercise such as running, bicycling, or stair climbing was especially detrimental to IVF outcomes. Women who did cardio for four or more hours per week for one to nine years were 50 percent less likely to have a successful pregnancy after their first IVF treatment than the women who didn't work out at all.
The findings were based on questionnaires given to 2,232 women before they underwent their first IVF cycle at one of three Boston-area clinics between 1994 and 2003.
It has long been known that a link exists between infertility and the intense physical activity common to professional athletes. "The ovaries are exquisitely sensitive," says Laurence Jacobs, reproductive endocrinologist and instructor of obstetrics and gynecology at the University of Illinois, who explains that neither extreme physical fitness nor lack of exercise leading to extra pounds is ideal for pregnancy. Many of his highly fit patients seeking fertility treatment are shocked at how difficult it is for them to get pregnant. For those women, he recommends reducing workouts to 30 minutes a day. Most are willing to do whatever it takes to help them get pregnant, but a small number prefer to keep up their avid pace. "It's their therapy."
The data should not be interpreted as a reason for women seeking IVF treatment to stop exercising altogether. "It's an important part of their life–it's a good part," explains Hornstein, who hopes the research will inspire other studies that investigate and decode the hormonal changes caused by varying degrees of exercise.
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