The daughters of women who took the drug DES during pregnancy face an increased risk of miscarriage or premature delivery when they themselves become pregnant.

The new finding of researchings at the University of California at San Diego, the University of Chicago and other medical centers is an ironic twist in the history of DES (diethylstilbestrol), a synthetic hormone taken during pregnancy by so many as 1.5 million American women because doctors mistakenly believed it prevented miscarriages.

Dr. Larry Cousins and co-workers at UC-San Diego studied 71 women who had been exposed to the drug because their mother took it while pregnant.

Comparing these "DES daughters" to a group of unexposed women, Cousins found that 40 percent of the DES group had premature babies and 25 percent of their babies died. The unexposed group had no premature births orinfant deaths. Thirty-five DES-exposed women had visible abnormalities of the vagina and cervix. Among them the figures were even higher: 71 percent delivered prematurely, and 43 percent of their babies died. h

While the San Diego researchers' results may be artificially high because of the way they chose patients -- most women were referred to the medical school by their doctors -- other DES experts are also finding that DES daughters have a higher risk of terminated pregnancies or delivering premature babies.

Dr. Arthur Herbst, the gynecologist who discovered in 1971 that DES had triggered cases of a previously rare vaginal cancer in young women exposed to it before birth, now believes the drug has caused an increase in premature deliveries, pregnancy loss and possibly infertility among other DES daughters.

In a study at the University of Chicago, Herbst has found, according to sources who have seen his data, that only 47 percent of DES-exposed women delivered full-term, live babies in their first pregnancy, compared to 85 percent of women not exposed to the drug. Twenty-two percent of the DES-exposed women delivered prematurely compared to 7 percent of unexposed women and 31 percent of the DES daughters miscarried during their first pregnancy or lost their babies, compared to only 8 percent of unexposed women.

Hebst said the reason why DES daughters may have problem pregnancies is unknown, but recommended that a woman mother took DES "should have increased medical surveillance" during her own pregnancy.

She should see her doctor more often than once a month, and the cervix -- the opening of the uterus -- should be watched carefully for premature dilation.

Because DES exposure before birth may have weakened the cervix, a DES daughter who has lost a pregnancy or shows abnormal dilation may need the cervix tied closed during the pregnancy. But he said such treatment is not routinely necessary for DES-exposed women, since most can have live babies without it.

DES, a synthetic form of the hormone estrogen, was prescribed to prevent miscarriages from the 1940s until the early 1970s, despite a controlled study at the University of Chicago in 1951-52 which showed it did not work. It is the daughters of those Chicago women -- half exposed to the drug, the other half not -- who participated in Herbst's most recent research.

DES along with other estrogens, is still approved by the Food and Drug Administration for symptoms in older women related to menopause, as a treatment for breast and prostate cancer, and for a few other conditions, although the drug label contains a warning about its ability to cause cancer of the uterus and forbids its use during pregnancy.

Until an EDA ban went into effect last year, it was fed to chickens and cattle as a fattening agent, and was therefore present in meat.

It is still prescribed by some doctors to women just after delivery to stop milk formation by the breast and as a "morning after pill" to prevent pregnancy.Neither of these uses is approved by the FDA.