Womb environment may affect timing of menopause

NEW YORK (Reuters Health) - Events surrounding a baby girl's birth may affect the age at which she later goes through menopause.

In a study of more than 20,000 middle-aged Puerto Rican and American women, researchers found that exposure in the womb to the man-made estrogen, diethylstilbestrol (DES), as well as certain characteristics of the mom, had small effects on the timing of this natural biological process.

"These aren't drastic changes, but the fact that something at birth can affect something 50 years later is fascinating," Dr. Anne Steiner of the University of North Carolina at Chapel Hill told Reuters Health.

A woman's ovaries hold the most eggs while she is in her mother's womb: about 5 million at 24 weeks gestation. By birth, she's left with roughly 2 million. The count continues to fall until menopause, when the last 1,000 eggs of her supply begin to run out and menstruation and fertility end.

This knowledge led Steiner and her colleagues to wonder if the womb might be a susceptible time period for women. Could things about her mom, the environment or the birth itself affect how many eggs a girl has when she's born? And might this subsequently alter her age at menopause?

According to the National Institute on Aging, 51 is the average age at which a woman reaches menopause (has her last period). But some women have their last period in their 40s and some have it later in their 50s.

About half of the women participating in the current study reached menopause before the age of 52, Steiner and her colleagues report in the American Journal of Epidemiology. And they found that certain characteristics and exposures appeared to bump up or push back this milestone.

After accounting for factors such as race, education level, family income and participant's smoking status, DES appeared to have the strongest effect on the age of menopause. Exposure to the hormone mimicker sped up the point at which a woman lost her last eggs by about a year. Decades ago, DES was prescribed to pregnant women with the thought that it would reduce the risk of miscarriage and nausea.

Being born at a low birth weight and whether or not a mother had diabetes prior to pregnancy were weakly linked to an earlier arrival of menopause of less than a year.

If a mother gave birth to a girl at the age of 35 or older, the researchers found a hint that menopause might be slightly delayed for that girl.

No effects of birth order, smoke exposure or breastfeeding were seen.

The researchers note that other factors may explain some of these differences. An older mother, for example, may simply pass down her ability to conceive at a later age -- reflective of a later onset of menopause.

"But the point is not one exposure or another," said Steiner. "It's more the idea that the rate we progress to the end of our reproductive life -- from puberty and ability to conceive to inability to conceive and menopause -- can be changed by such early events."

SOURCE: link.reuters.com/ner36m

American Journal of Epidemiology, online June 9, 2010.