I have previously written about the impact of obesity on IVF pregnancy rates. In fact, IVF pregnancy rates are 68% lower in morbidly obese patients. Several studies have shown that obesity is associated with hormonal abnormalities and a decreased response to fertility drugs. This results in fewer eggs being harvested. The egg retrieval and embryo transfer can also be difficult in obese patients. Researchers from Harvard Medical School have now shown another mechanism that may contribute to the lower success rate: Obese women are more likely to have abnormalities in their eggs that make them impossible to fertilize.
Machtinger et al. (Human Reproduction; Advance Access publication on Sept 11, 2012) examined nearly 300 eggs that failed to fertilize during IVF in both severely obese women and those with a normal body weight. They found that severely obese women were far more likely to have abnormally arranged chromosomes within their eggs compared with women who weren’t overweight.
Researchers still don’t completely understand why obesity might lead to structural problems in eggs, but it could have something to do with higher levels of hormones like leptin, which make chromosomes more fragile.
The women in the study were severely obese with a body mass index of at least 35 -- or 210 pounds for a 5-foot, 5-inch person -- and it’s likely that moderately overweight women who carry just 20 or 30 extra pounds don’t have the same increase in egg abnormalities.
Older women have similar abnormalities with aging eggs and therefore have trouble conceiving. It is not possible to turn back the clock in these women. However, it may be possible to improve egg quality by achieving a healthier lifestyle. It is well-established that even a 5 – 10% weight loss may improve outcomes.
The study has the following limitations: only failed fertilized eggs were studied, the sample size is small and there may be other unknown factors that could affect outcome. The authors also state that it is unclear whether the findings are applicable to successfully fertilized eggs. It is also not clear as to whether this egg-level problem is present in patients that are not stimulated with fertility drugs.
This is another reason why obese patients should lose weight.
Dr. Karande is Board Certified in the specialty of Obstetrics and Gynecology as well as the subspecialty of Reproductive Endocrinology and Infertility. He is a Fellow of the American College of Obstetricians and Gynecologists and Member of the American Society for Reproductive Medicine.