Race and ethnicity may be important factors in women’s reproductive lives, from the timing of the first menstrual period to the severity of menopausal symptoms, a new research review finds.

A growing number of studies in recent years have found racial and ethnic disparities in women’s reproductive health, but the reasons remain unclear.

In the new review, published in the journal Fertility and Sterility, researchers found that in general, race and ethnicity affected the timing of puberty, the odds of successfully becoming pregnant through fertility treatment and the transition into menopause.

Compared with white women, black and Hispanic women typically started menstruating at an earlier age, while Asian women tended to start later - though the data on that last finding are conflicting.

Several large U.S. studies suggest that black girls start to show signs of puberty about one year earlier, on average, than white girls - around age 9, versus age 10 - and start menstruating close to a year earlier. Hispanic girls tend to fall somewhere in between.

A few reports suggest that Asian girls typically hit puberty later than white and Hispanic girls. One U.S. study, however, found that girls of Asian descent began menstruating at a slightly earlier age than white girls.

The reasons for these racial and ethnic differences are not certain, according to Dr. Samantha F. Butts, of the University of Pennsylvania in Philadelphia, and Dr. David B. Seifer, of Mt. Sinai School of Medicine in New York.

One possibility, they write, is the difference in rates of childhood obesity, since greater fat mass may spur earlier puberty. On the other hand, there is evidence that earlier puberty contributes to excessive weight gain thereafter. It remains unclear which comes first, according to Butts and Seifer.

When it comes to assisted reproduction, a number of studies - though not all - have found that black women have lower success rates than white women. In one U.S. study, for example, the birth rate among black women undergoing their first cycle of fertility treatment between 2004 and 2006 was 22 percent; that figure was 32 percent among white women.

Few studies on assisted-reproduction outcomes have included Hispanic and Asian women, but some suggest that these women also have a lower success rate than white women.

Again, Butts and Seifer write, the reasons for these findings are unknown. One possibility is that minority women have less access to fertility treatment, and may have longer-standing infertility by the time they do get help. Differences in the underlying cause of the infertility, lifestyle habits or genetics could also be at work, the researchers note.

Finally, when the investigators looked at menopausal symptoms, they found that black women were generally more likely than white women to suffer symptoms like hot flashes, night sweats and vaginal dryness, while rates tended to be lowest among Asian women.

Obesity may, again, be a factor, since body fat levels affect hormone balance. However, Butts and Seifer write, studies suggest that even when body fat is taken into account, race itself seems to influence menopausal symptoms.

As for the timing of menopause, there is some evidence that black women begin menopause earlier than white women. However, there is not enough research to draw firm conclusions yet, according to the report.

More studies, Butts and Seifer write, are needed to tease out the various reasons for racial and ethnic differences in reproductive function - and to, when possible, improve minority women’s fertility treatment outcomes and management of menopausal symptoms.

SOURCE: Fertility and Sterility, online November 24, 2009.