Accutane, a drug introduced in 1982 for use in severe cases of acne, is among the most dangerous medications to take during pregnancy, a new study concludes.

Of 154 pregnant women who took the drug inadvertently, 12 had miscarriages, 21 delivered babies with birth defects, and 26 had normal infants. The other 95 chose to have abortions after learning of the risk, The New England Journal of Medicine reports.

Such a high rate of birth defects puts the drug in a class with thalidomide, which caused an estimated 8,000 severe birth defects in Europe in the late 1950s.

A key difference, however, is that Hoffmann-LaRoche Inc., maker of Accutane, and the Food and Drug Administration have warned since its introduction that pregnant women should not take it. Women are also told to use birth control during treatment. The journal points out, however, that with 10,000 new women of child-bearing age receiving the drug every month, mistakes can occur.

Birth defects included malformations of the head, face, heart, central nervous system and thymus -- a gland that regulates growth.

"We found that 67 percent of the exposed pregnancies were among women who were either pregnant when therapy began or were not using contraception," Dr. Edward J. Lammer and 11 other researchers write. "These exposures could have been prevented if the guidelines for treatment in women had been followed."

If a women becomes pregnant during treatment, they write, abortion should be considered.