Researchers have found that women who continue to exercise while they are trying to conceive using IVF may reduce their chances of conception. The research, published in the October issue of the journal Obstetrics & Gynecology, found that women who regularly exercised for more than four hours per week - and who had done so for one to nine years previously - were 40 per cent less likely to have successful IVF treatment than women who didn't exercise.

The data showed that, in particular, intense cardiovascular exercise such as running, cycling and stair climbing, was detrimental to IVF outcomes. The findings were based on responses to questionnaires filled out by 2,232 women undergoing their first cycle of IVF at one of three fertility clinics in the Boston area between 1994 and 2003. It has long been known that there is a link between infertility and the kind of intense physical training undertaken by professional athletes, and these findings seem to suggest that this may extend beyond such women. 'The ovaries are exquisitely sensitive', explained Laurence Jacobs, reproductive endocrinologist and instructor of obstetrics and gynaecology at the University of Illinois, who also pointed out that neither extreme physical fitness nor lack of exercise leading to extra pounds is ideal for pregnancy. He suggests that women who exercise strenuously and find it difficult to get pregnant should work out for only about 30 minutes per day.

However, the researchers also found that women who had followed a strict fitness regime for between 10 and 30 years were as likely to have successful IVF treatment as women who did no exercise.

The researchers suggest that excessive exercise can put stress on a woman's reproductive system, which makes her body 'protect' itself from a pregnancy. Mark Hornstein, the lead researcher and clinical director of reproductive endocrinology at Brigham and Women's Hospital in Boston, said that this might be because of subtle hormonal changes caused by exercise. But when asked why this effect appears to change after 10 years, he said 'we don't have a good answer for that', adding that 'it may be that the body accommodates'. He added that the research findings should not encourage women seeking fertility treatments to stop exercising altogether: 'our findings are not strong enough to encourage women to abandon exercise and embrace a sedentary lifestyle', he said. Hornstein also said that he hopes that the research will inspire further studies into the hormonal changes caused by varying degrees of exercise.

Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.