'The data seem to suggest notable effects of the month/season of birth on the length of a woman's fertile life, further supporting the role of environmental factors in regulating reproductive life and the timing of its termination.'

This adds to a large body of work finding that prenatal growth influences the future fertility of both men and women.

"Mothers should be aware of this, considering that during pregnancy they are going to influence not only the health of the newborn, but also the health and reproductive life of their child during adulthood," said Dr. Angelo Cagnacci, an associate professor of obstetrics and gynecology at the University of Modena in Italy and lead author of the study.

It appears Thursday in the May edition of Human Reproduction, a monthly journal published by the European Society for Human Reproduction and Embryology.

On average, there was 18 months' difference in onset between women born in October, reaching menopause at an average age of 50 years, 3 months, as opposed to 48 years, 9 months for women born in March. The researchers found no relationship between the month of birth and when women began menstruating.

The study, carried out at four university hospitals, looked at the records for 2,822 women, with an average age of 53 at the time of the research, who were at least a year into their menopause.

Cagnacci said the team controlled for other factors likely to influence timing of menopause -- including weight, smoking and the age when menstruation began -- and still found that menopause was conditioned by month of birth. The number of pregnancies a woman had did not affect the timing of menopause.

The study showed that the average age for onset of menopause among all the women was 49.42 years.

Cagnacci said it was possible that some women did not accurately recall the exact timing of reproductive changes, and he noted that the study involved women referred to menopause centers for care rather than to those in a general population. Women living elsewhere in the world might also be affected differently, he added.

"Nevertheless, the data seem to suggest notable effects of the month/season of birth on the length of a woman's fertile life, further supporting the role of environmental factors in regulating reproductive life and the timing of its termination, " he said.

Researchers don't know exactly how seasonal environmental factors affect offspring in the womb and perhaps even before conception.

They speculate that differences in temperature or sunlight may influence fetal growth and future reproductive potential. Or there may have been diet differences or exposure to infections that varied according to season and influenced later reproductive development.

"Our data seem to indicate that women born in autumn develop better during their prenatal life and are born with a higher number of oocytes (eggs) than women born in spring," Cagnacci said.

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