Menopause usually occurs around the age of 50. But early menopause, or premature ovarian failure (POF), can occur at a younger age. In about one woman in a hundred it happens before the age of 40.

"There appears to be generally a higher probability of premature ovarian failure in twins, both identical and non-identical," said Dr. Roger Gosden of the Weill Medical College of Cornell University in He and his team, who studied more than 800 pairs of twins in Australia and Britain, found POF at the age of 40 and 45 was three to five times more common in twins than in other women.

The findings, which are reported in the journal Human Reproduction, were based on an analysis of data on 428 twin pairs in Australia, 404 sets of twins in Britain and information on 3,483 Dutch women who acted as a control group.

The researchers compared the menopausal age of the women in the three groups to determine any significant variations in the twins.

"There is about a three to five fold increase in the probability of having premature ovarian failure," Gosden said in an interview.

Age at menopause inherited
Previous studies in twins and mothers and daughters suggested menopausal age was inheritable. So the age at which the menopause occurred was similar between twin sisters and mothers and daughters.

The causes of premature ovarian failure are unknown. The ovaries do not function properly because of a lack or depletion of eggs and the menstrual cycle stops.

Hormones, genes, the immune system as well as other factors may play a role. There are cases of POF in which the menstrual cycle returns but if there are no eggs left infertility occurs. There is no effective treatment to restore the function of the ovaries. Scientists are working on ovarian transplants but they are still experimental procedures. Hormone replacement therapy is often advised to relieve symptoms of POF which can include hot flashes, night sweats and irritability.

Gosden said his findings are consistent with earlier research because identical twins in the study had fewer discrepancies in menopausal age than non-identical twins. In a few cases there was a 20-year discrepancy in the age of menopause among non-identical twins.

Gosden stressed that although twins have a higher risk of POF, it is still small.

"We're still talking about an unusual phenomenon. Most twins of both types will normally have their menopause around the typical age of 50-52," he added.