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Fertility treatment success linked to weight and race, study claims

14 February 2011
Appeared in BioNews 595

New research suggests that women from ethnic minority backgrounds may have lower success rates with fertility treatment.

Research has already shown that there are important racial and ethnic differences, with particular minority groups experiencing a greater risk of 'adverse reproductive outcomes', including low birth weight and higher infant mortality. However, these disparities are just emerging and less well established among women undergoing fertility treatments, namely IVF. It has been suggested that higher rates of obesity among women from minority backgrounds may be a contributory factor in these differences.

To address this question, scientists collected information on nearly 32,000 fertility procedures performed at US clinics in 2007. They found that obese women were less likely to have a baby compared to normal weight women. However, even when weight was accounted for, black, Hispanic and Asian women still had lower success rates compared to white women. Following IVF treatment, 45% of white women became pregnant, compared to 43% of Hispanic women, 38% of Asian women and 36% of black women.

Further differences were also observed in maintaining the pregnancy and giving birth: 85% of white women who carried their babies for at least 22 weeks eventually gave birth, compared to 80% of Asian and Hispanic women and 76% of black women.

These results more firmly establish a racial disparity in reproductive success among women receiving fertility treatment and refute the notion that weight differences are responsible. This leaves the question of what other factors could account for these discrepancies.

The team led by Dr Barbara Luke of Michigan State University suggests a few possibilities. One potential explanation could be body fat distribution. Increased body fat is thought to affect reproductive success by altering hormone levels and increasing inflammatory factors. Although overall body fat did not explain the differing success rates, the distribution of fat may do. Black women tend to carry more of their excess weight in the upper body, which is thought to bear greater health risks 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. The scientists also speculate a role for vitamin D deficiency, which has been linked to an increased risk of a vaginal infection called bacterial vaginosis, increasing the chances of complications during pregnancy.

Individuals are able to synthesise vitamin D endogenously when their skin is exposured to sunlight. However, increased pigmentation in darker skinned people can hinder this process and can lead to deficiency in countries where sunlight is less abundant.

Other factors such as age and type of infertility did not explain the racial differences either. However, the research team was restricted by the limited amount of available information on the women.

The researchers called for further studies to be carried out, where 'future research', they suggested, 'should focus on clarifying the underlying causes of these disparities'.

The findings were published in the journal Fertility and Sterility.

Racial and ethnic disparities in assisted reproductive technology pregnancy and live birth rates within body mass index categories
Fertility and Sterility |  27 January 2011
Weight, race tied to fertility treatment success
Reuters |  9 February 2011
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