Twins are more likely to experience early menopause than other women, according to a recent study led by Prof. Roger Gosden, reproductive biology, at the Weill Cornell Medical College in New York City.
Gosden and his colleagues found that twins are three to five times more likely to develop premature ovarian failure (POF) than the general population. Though that may sound like an enormous increase in risk for twins, Gosden emphasized that POF is still extremely rare: it occurs in about one percent of the general population, so it only occurs in three to five percent of twins.
The surprising element of the study’s findings was that identical twins were just as likely to develop POF as fraternal twins. There is a reasonable explanation for fraternal twins to have early menopause, but this explanation does not carry over to identical twins.
Fraternal twins could be inheriting their mothers’ genetic predisposition to early menopause. “Fraternal twinning peaks at about 36 years, past the peak age of childbearing,” Gosden said.
A woman has fraternal twins when two different eggs are fertilized and implant themselves in her uterus at the same time. This is more likely to happen towards the end of a woman’s reproductive cycle, when her ovarian reserve is running low and her body is producing more of the hormone that brings eggs to maturity, encouraging her to have children while she still can.
Since a woman is born with all the eggs she will ever have, she could be more likely to experience early menopause simply by being born with fewer eggs. This would make her more likely to have twins at a younger age.
POF can also run in families, according to Gosden. “If a woman’s mother or aunt has menopause start at, say, 45, that woman is more likely to have early menopause than a woman whose mother started menopause at 52,” he said.
The higher-than-normal frequency of POF among fraternal twins could therefore be explained by the fact that women who are prone to early menopause are more likely to have twins in the first place.
The likelihood of having identical twins, however, does not depend on age. Women with a tendency towards premature menopause are not more likely to have identical twins, so this hypothesis does not explain the higher incidence of POF in identical twins.
The “greatest mystery” brought up by this study is that sometimes one identical twin will start menopause 20 to 25 years before the other does. Fortunately, there are practical implications of the study that can help twins in this situation: an ovarian tissue transplant can completely reverse POF within a few months. This study was prompted in part by a successful example of this procedure. A few years ago, Gosden and his colleagues were approached by a 24-year-old identical twin who had stopped menstruating when she was 14 and wanted to have a child. After trying and failing to conceive using in-vitro fertilization, the woman and her twin sister decided to try an ovarian tissue transplant, in which the fertile twin, who already had three healthy children, donated tissues from one of her ovaries to her sister. The largely experimental procedure worked beautifully: the woman began menstruating normally again after only three months, and about a year later gave birth to a healthy daughter. The details of this case were published by Sherman J. Silber in the New England Journal of Medicine on July 7, 2005.
Gosden and his colleagues studied the records of over 800 twins from the Australian and United Kingdom national twin registries, paying special attention to how many of the women had reached menopause at ages 40 and 45. Their findings were published in the European journal Human Reproduction on October 25, 2006.