The daughters of 1000 New Zealand women who were prescribed a synthetic estrogen are at a higher risk of cancers, infertility and premature births, a new study shows.

A study in the New England Journal of Medicine examined women who were exposed in the womb to diethylstilbestrol (DES), which was prescribed in the mistaken belief it could reduce pregnancy complications.

Researchers at the National Cancer Institute and other medical centers followed 4,600 women who were exposed to DES before it was discontinued in 1971.

They found daughters who were exposed to the drug had an increased risk of 12 medical conditions, including a twofold higher risk of infertility and a fivefold increased risk of having a preterm delivery.


The women also had 40 times the risk of developing a rare cancer of the vagina among young women, called clear cell adenocarcinoma, and breast cancer, the researchers said.

New Zealand drug regulator Medsafe said DES was the active ingredient in a drug called Stilboestrol, which was given to an estimated 1000 pregnant New Zealand women before 1971.

Its statement said the Ministry of Health asked GPs to contact patients who may have been prescribed Stilboestrol during pregnancy in 1989.

An information sheet was prepared for mothers prescribed Stilboestrol to help them discuss their "health monitoring requirements".

Despite that, Ministry of Health records indicate that Stilboestrol tablets was used routinely to treat prostate cancer until 1991, Medsafe said.

Manufacture was stopped in 1996 and no other products containing DES have been approved since.

Between five and 10 million pregnant women and babies have been exposed to DES in various forms, including pills, creams and vaginal suppositories.

Study author Robert Hoover at the cancer institute, part of the National Institutes of Health, said his study was the first to show the full array of risks presented to women who were exposed to DES.


It revealed that one of five DES-exposed daughters will experience some level of infertility.

They are also more than twice as likely to develop pre-cancerous cells in the cervix or vagina and have an 80 percent higher chance of developing breast cancer after age 40, the study found.

According to the researchers, one in 25 DES-exposed daughters will develop abnormal cellular changes in the cervix or vagina, and one in 50 will develop breast cancer due to their DES exposure by age 55.