Is it really safe for women to have sexual intercourse while pregant? A new study indicates not. The study, based on a review of 26,868 pregnancies, found that newborn infants were two to three times more likely to die from infection if their mothers had sex during pregnancy. Women who had intercourse while pregnant were one-third more likely to develop an infection, and when an infection did occur it was almost five times as likely to kill the fetus.

Such infections, involving the amniotic fluid -- the liquid thats surrounds the fetus -- caused 17 percent of the infant and newborn deaths in the United States during the period of the study, 1959-66.

Dr. Richard L. Naeye, who published his results in the New England Journal of Medicine, noted that since then the infant death rate has decreased and "deaths from coitus-related infections may be less frequent today." He also suggested that the infection risk could be reduced by cleanliness and the use of prophylactics. The study found that there were 156 cases of infection for each 1,000 births when women had intercourse one or more times a week during the month before delivery. Among women who abstained, there were 117 cases of infection. The danger was greatest midway through pregnancy and decreased somewhat as the fetus matured.

Ordinarily, the amniotic fluid is able to resist infection unless it is overwhelmed with bacteria. Naeye theorized that the wiggling motion of the sperm or the protein-destroying enzymes in semen may help bacteria penetrate the cervical opening and get into the womb.