A study of 4000 women in the U.S. has found that those whose mothers smoked during pregnancy were 21 percent more likely to have gone through menopause at any given age. Researchers had followed the women in the study since the 1970s.

Mothers' smoking during pregnancy appears to "program" female children's eventual age at menopause in some way, according to the researchers' report in the American Journal of Epidemiology.

Dr. William C. Strohsnitter, of Tufts-New England Medical Center in Boston, led the study.

Previous research had shown that women who smoke tend to go through menopause at a younger age. It may be that cigarette smoke affects estrogen production, or the ovarian follicles producing women's eggs each month. But the fact that maternal smoking can affect daughters' menopause cycle is new.

It has long been know that women are born with a certain number of ovarian follicles. According to Strohsnitter and his colleagues, what is less clear are the prenatal factors that may influence this number.

To investigate, the researchers used data from a study begun in 1975 to study the effects of prenatal exposure to DES, an oral estrogen that was once prescribed to prevent miscarriages but was later found to be linked to a rare vaginal cancer in young women whose mothers used the hormone.

Strohsnitter's team focused on 4,025 participants in a study begun in 1975 and originally designed to track the effects of prenatal exposure to DES, the oral estrogen that was found to be linked to a rare form of vaginal cancer. The women in Strohsnittter's study were born between 1939 and 1968 and were chosen because they had complete information on their mothers' smoking.

The researchers found that, at any given age, women whose mothers had smoked during pregnancy were more likely to have reached menopause than women whose mothers did not smoke, regardless of other factors.

It may be that prenatal exposure to tobacco smoke affects the early development of ovarian follicles, but the researchers warn that more studies are needed to determine if this is the case.