Regardless of weight, black, Hispanic and Asian women had lower success rates than white women. Overall, 45% of white women became pregnant, versus 43% of Hispanic women, 38% of Asian women and 36% of African Americans.
Fertility treatments were about 20% more likely to fail in obese women. Researchers have recognized this problem for a while now; not long ago, US scientists reported that certain fertility drugs could help bring success rates in obese women up to equal those in normal-weight women.
The findings, reported in the journal Fertility and Sterility, not only bolster evidence that excess weight may hinder the success of infertility treatments. They also back up previous studies showing that women of other races have less success than white women.
Studies have found that obese women, in general, have a harder time becoming pregnant than thinner women - possibly because of how excess fat affects hormone levels or low-level inflammation throughout the body.
As for racial differences in fertility treatment success, one potential explanation could be body-fat distribution. Compared with white women, black women tend to carry more of their excess weight in the upper body, where it is believed to create more inflammation and greater health risks in general than fat around the hips and thighs. Black women are also more likely to have uterine fibroids, which are associated with lower pregnancy and birth rates.
Factors like age and the type of infertility did not explain the racial differences, but the researchers were limited in the information they had on women in the study.
That means more studies are needed to specifically address the race question in fertility treatment success, the researchers say.
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