Doctors in a new analysis have found that women who are obese and use donor eggs don't necessarily have poorer odds of getting pregnant using assisted reproductive technologies.¹

Discordant Research
Richard Scott, MD, with Reproductive Medicine Associates of New Jersey and a team of colleagues from Emory University wrote that while previous studies have shown that obesity lowers the odds of an embryo implanting in the uterus, as well as a subsequent pregnancy, other studies failed to show that obesity increases the risk of miscarriage.

"The question remains as to the mechanism in which obesity may affect [fertility] in women," the researchers wrote. "Is it exclusively an ovarian effect, endometrial effect, or a combined effect?" The answer to this question remains elusive because few other studies have looked at the possible cause behind obesity's role in pregnancy success using assisted reproduction, Scott and his colleagues wrote.

Does Egg Donation Make a Difference?
In hopes of clearing up the confusion, Scott's team evaluated records of patients involved in egg donation at the New Jersey clinic to determine whether obesity had an effect on assisted reproductive technology (ART) outcomes in those cases.

In all, information on 536 patients who underwent ART using donated eggs between 1999 and 2004 was analyzed. All of the patients were considered healthy at the time, and were under 32 years of age. Scott and his colleagues evaluated information such as age, weight, height, the number of embryos transferred to each patient, the day of embryo transfer after fertilization, endometrial thickness, and pregnancy, implantation, and miscarriage rates.

Information on each woman's body mass index (BMI), which is a measure of healthy weight corresponding to height, was collected, and then divided into four categories: underweight, normal weight, overweight, and obese.

All patients had undergone standard ovulation induction and in vitro fertilization (IVF). Embryo transfers were performed either three or five days after fertilization.

Similar Outcomes, Regardless of Weight
The researchers found that about 14 percent of the patients were considered obese, with BMIs of 30 or more. After comparing the four different weight groups, there were no significant differences in either implantation or pregnancy success between any of them. Those considered obese had an implantation rate of about 55% and a pregnancy rate of 74%. That compares to an implantation rate, on average, of about 54% in those classified as underweight, normal weight, or overweight. Similarly, approximately 73 percent of the women in those three groups became pregnant, on average.

Embryo Transfer Protocols and Miscarriage
The researchers broke the data down even further, analyzing the rates of embryo implantation and pregnancy between those women who had transfers three days after fertilization, or five days later. Again, women who were considered underweight, normal weight, overweight or obese generally had similar outcomes.

Scott's group also looked for a possible effect that obesity might have on the odds of miscarriage, and found none in the records they reviewed. "BMI does not appear to be a risk indicator of spontaneous loss," Scott and his team wrote.

"In our study, elevated BMI was not associated with implantation failure, decreased pregnancy rate, or higher [miscarriage] rate," the investigators concluded.

Flawed Findings
Scott and his colleagues cited one other study that found obese women using egg donation did face a higher risk of miscarriage.² However, the findings were flawed, they point out, since some patients underwent more than one cycle due to conception failure or miscarriage, weighing the results toward that group. "This is a common mistake that we have found in our review of the literature, and it may explain why there is so much controversy regarding this topic," Scott and his team wrote.

There have been studies suggesting an increased risk of miscarriage in obese women using their own eggs, but that may be due to poor egg and/or embryo quality, the researchers speculated. To control for that in this study, Scott and his colleagues reviewed cases in which egg donation was made by younger women with normal weight.

"Based on this information, we can comfortably counsel our [egg] recipients that elevated BMI will have no direct effect on their implantation rate and ability to sustain a pregnancy," the research team concluded.

1. Styne-Gross A, Elkind-Hirsch K, Scott RT Jr. Obesity does not impact implantation rates or pregnancy outcome in women attempting conception through oocyte donation. Fertil Steril 20905 Jun;83(6):1629-34.
2. Bellver J, Rossal LP, Bosch E et al. Obesity and the risk of spontaneous abortion after oocyte donation. Fertil Steril 2003 May;79(5):1136-40.

John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.