WEDNESDAY, Oct. 25 (HealthDay News) -- Twin sisters face triple the odds of entering menopause prematurely compared to women who don't have a twin, researchers report.
"It's a three-to-five-fold increase in risk of having menopause before the age of 40," said study lead author Roger Gosden, director of reproductive biology at Weill Cornell Medical College in New York City. However, he added, "We have to bear in mind that over 95 percent of women who are twins will still have menopause at the normal time. There shouldn't be any general alarm."
The study was published Wednesday in the Oct. 25 online edition of Human Reproduction.
Overall, about 1 percent of adult women have premature ovarian failure (POF), prompting menopause before the age of 40. Not only does this affect fertility, but it may also boost risks for cardiovascular disease and osteoporosis.
The mean age of menopause is 50 to 52 years.
Gosden had already published research on a twin who underwent POF at age 14. The woman's twin, however, remained fertile and was able to donate ovarian tissue to her sister for a transplant.
"It was that study that stimulated us to do this big survey and to find out how common early menopause is in identical twins and how often there may be discordances," Gosden explained.
There had already been hints in the medical literature that fraternal twins might be at higher risk of early ovarian failure. The current study confirmed that and added new information about identical twins.
In all, the researchers looked at 428 twin pairs from an Australian twin register and 404 from a British twin registry. These were compared to a control group of 3,483 Dutch women. Women who had undergone a hysterectomy were automatically excluded.
Rates of POF were similar in both registries and three-to-five times higher than the general population at ages 40 and 45. This was true of both fraternal and identical twins.
But in some cases, the twin pairs had very different ages of menopause, sometimes varying by as much as 20 years.
"The biggest mystery surrounds the identical twins because one would expect them to have similar menopause," Gosden said. "That is true most of the time, but, in some cases, it's extraordinarily early and may be different from the other twin."
The reasons are unclear. However, Gosden said that scientists "know why identical twins [can be] very different in terms of their ovaries."
"We do believe that the problem starts when the woman was actually a fetus, when the eggs were formed," he continued. "We believe that the infertile sister doesn't form a normal number of eggs, so she runs out of eggs earlier."
"The ovary works like an hour glass with a fixed number of eggs," Gosden explained. "When they've run out, the woman has menopause. We believe that the infertile twin has fewer eggs to begin with."
Now Gosden is moving his research into the clinical stage.
"We've been receiving calls from twins where one has had an early menopause, and they're interested in having a transplant from a fertile twin to an infertile twin to restore ovarian function," Gosden said. So far, 10 patients have signed up, five of whom have already had transplants. All the transplants have been successful, and three women have become pregnant or delivered babies.
"One of the important things to take out of this study is that one twin could serve as an egg donor or donor of ovarian tissue in order to reverse early menopause for the other twin," said Dr. Jennifer Wu, an obstetrician/gynecologist at Lenox Hill Hospital in New York City. "We have so many advances these days in regard to fertility, so premature menopause is not the terrible thing it once was."
More information
Learn more about menopause at the North American Menopause Society.
SOURCES: Roger Gosden, Ph.D., director of reproductive biology, Weill Cornell Medical College, New York City; Jennifer Wu, M.D., obstetrician/gynecologist, Lenox Hill Hospital, New York City; Oct. 25, 2006, early online edition, Human Reproduction
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