Studies have shown that obesity is associated with lower chances of pregnancy using IVF, but most of this work is limited to women using their own eggs. Research on outcomes for obese women using donor eggs has had mixed results.

The new analysis by investigators at Washington University School of Medicine in St. Louis and the University of California-Los Angeles pooled and analyzed data from more than 4,700 women in earlier studies.

The results are available online in the journal Human Reproduction.

"Our study suggests that obesity does not significantly affect whether a woman will become pregnant with donor eggs," said first author Emily Jungheim, MD, assistant professor of obstetrics and gynecology at Washington University School of Medicine. "This supports the argument that doctors shouldn't discourage obese women from pursuing treatment if they need donor eggs to conceive."

The report, a meta-analysis, included patients from five earlier studies conducted over the past decade, in addition to data from 123 egg donor recipients from the Washington University Infertility and Reproductive Medicine Center.

Many IVF programs have arbitrary body mass index (BMI) restrictions that help them determine whether women can receive treatment. These cutoffs, according to Jungheim, need to be re-examined. "There's still a lot about obesity that we don't know when it comes to reproduction," she said.

Investigators aren't sure whether the quality of a woman's eggs or her uterus are most affected by obesity. As a result, several studies have focused on donor egg recipients to provide some clues.

In this analysis, obesity (defined as a BMI over 30) was not associated with a difference in pregnancy rates when compared with pregnancy rates in women with a normal BMI. The data from this study also indicates that obesity was not associated with differences in the rates of miscarriage or live birth among obese women who used donor eggs, when compared with women of normal weight. However, live births and miscarriages were not reported in all of the studies.

"In general, most obese women who want to get pregnant are eventually able to conceive," Jungheim said. "We need to find out what specifically goes wrong in obese women who don't. We think other factors besides BMI are involved."

Funding for this research comes from the Women's Reproductive Health Research Program of the National Institutes of Health (NIH). NIH Grant number (K12HD063086).