Boston: Exposure to a common pregnancy drug has been linked to an early menopause for babies exposed to it in the womb, according to a new US study.

The drug, known as DES, an artificial form of oestrogen, was given routinely to women between the 1940s and 1970s to prevent miscarriages. The drug. also known as diethylstilboestrol/Stilbeostrol, was withdrawn in the seventies after it was found to cause defects in children.

But a study of thousands of women by Boston University has revealed that those who were exposed to it in the womb were 50 per cent more likely to start the menopause early.

In addition the women who took it are also at an increased risk of breast cancer, and this risk has likely been passed onto their daughters.

DES was withdrawn after many female children developed cancers of the vagina and other disorders of the reproductive system which made them infertile. The sons had low sperm counts and undescended testicles, and it is thought they might be at increased risk of testicular cancer.

Studies have shown that mothers and daughters both have an increased risk of breast cancer, with the risk increasing with age.

For instance, DES daughters over 40 have almost twice the usual risk of developing the disease. The latest study is the first to look at whether exposure to DES affected a woman’s reproductive life.

The researchers compared the age of menopause of 4,800 ‘DES daughters’ with that of more 2,100 women whose mothers had not taken the drug. The DES daughters were 50 per cent more likely to have reached menopause early. And the more DES their mothers had taken, the greater the risk. Worst affected were those whose mothers had taken part in a DES trial in the Fifties – these women were twice as likely to have reached menopause as others their age.

The increase in risk, the American Journal of Epidemiology reports, is thought to be because DES reduces the number of immature eggs produced as the unborn baby develops in the womb.

Baby girls are usually born with up to two million eggs but by the time they reach menopause all but 1,000 or so have withered away. If DES daughters have fewer eggs to begin with, they might reach menopause earlier.

Lead researcher Professor Julie Palmer, who has studied the effects of DES for 14 years, said that every woman who knows she is DES exposed should be having careful screening for vaginal cancer.

Women who took the drug and the children of these women should seek advice from their doctors.