Using frozen embryos may level the playing field for African-American and white women undergoing in vitro fertilization, a new study suggests, despite earlier research showing that African- American women have lower success rates with the procedure than white women do.

The findings, reported in the journal Fertility and Sterility, may ultimately help shed light on the reasons for the racial disparity seen in past studies of in-vitro fertilization (IVF), which costs thousands of dollars per “cycle” and is often not covered by insurance.

A number of studies, though not all, have found that black women tend to have a lower pregnancy rate following IVF than white women do. But most of those studies have looked at IVF done with “fresh” embryos, implanted a few days after the woman’s eggs have been retrieved and fertilized in a lab dish.

The current study focused on 169 women at one infertility clinic who had undergone fertility treatment with stored, frozen embryos created from their own eggs.

It found that African-American and white women were similarly likely to have a baby: 28 percent and 30 percent, respectively, gave birth - a tiny difference that was likely due to chance.

In contrast, the pattern was much different when the researchers looked at data on the women’s initial IVF attempts using fresh embryos: 40 percent of white women had a baby following that round of treatment, versus only 17 percent of African Americans.

The findings raise questions about one of the proposed reasons for black women’s generally lower IVF success rates, according to the researchers, led by Dr. Alicia Y. Armstrong of the U.S. National Institute of Child Health and Human Development.

That theory holds that black women’s significantly higher rate of uterine fibroids - non-cancerous growths in and around the walls of the uterus - may explain the lower IVF success. In the current study, 40 percent of African-American women had uterine fibroids compared with only 10 percent of white women.

But if uterine fibroids were the key factor, then black women’s birth rates should have been lower than white women’s, regardless of whether fresh or frozen embryos were used.

“This suggests that it’s probably not fibroids alone,” Armstrong told Reuters Health.

One possibility, she said, is that women of different races and ethnicities respond differently to the fertility drugs given to stimulate their ovaries to produce eggs. Those drugs would be given during the initial, fresh-embryo treatment cycle, but not later attempts using frozen embryos.

Race-based differences in women’s hormonal responses to those medications could potentially affect the odds of the embryo successfully implanting in the uterus or the chances of maintaining the pregnancy.

The findings, according to Armstrong, should be helpful in directing future research into the underlying causes of racial disparities in IVF outcomes. It may turn out that for African-American women who fail to give birth after a first IVF attempt, the next attempt should be made with frozen embryos stored from the original round of treatment, Armstrong noted.

However, she said, larger studies that follow women over time are needed to see whether that is the case.

For now, Armstrong recommended that women undergoing fertility treatment discuss all of the personal factors that could affect their odds of success, so that they go into it with the most realistic expectations possible.

SOURCE:  Fertility and Sterility, online May 7, 2010.