Solvents' link to birth defects bolstered

Science News, March 27, 1999 by N. Seppa

Since 1985, researchers at the Hospital for Sick Children in Toronto have offered a program called Motherisk for women in their child-bearing years who are concerned that they have been exposed to harmful chemicals or radiation.

Now, potent evidence that Motherisk researchers accumulated over 10 years indicates that many women have good cause for worry.

Pregnant women exposed to organic solvents are indeed much more likely to have a deformed baby than unexposed women are, the scientists report in the March 24/31 Journal of the American Medical Association.

Between 1986 and 1996, the investigators tracked and recorded the outcomes of pregnancies in 125 pregnant women exposed to organic solvents at workplaces such as factories, laboratories, graphic design businesses, and print shops. The solvents included phenols, xylene, acetone, and trichloroethylene.

The women were exposed for at least 4 months of their pregnancy, including the entire first trimester, says study coauthor Sohail Khattak, a pediatrician and clinical pharmacologist at the hospital. The first trimester is a critical time during which organs form in a fetus, he explains.

Khattak and his colleagues also tracked 125 pregnant women who had sought advice from Motherisk doctors for what turned out to be harmless exposures to chemicals, such as taking acetaminophen during pregnancy. These women were matched to the exposed group by age and lifestyle.

Most of the women in both groups were referred to Motherisk by their doctors, but some came in on their own.

Of 113 live births to the women exposed to the chemicals, 13 babies--12 percent of births--had major malformations, such as deafness or a heart defect. Five other babies had minor birth defects. Twelve of the pregnancies ended in miscarriage or abortion.

Women in the control group had 115 live births, but only one baby had a major birth defect and one had a minor deformity.

Among healthy mothers such as these, the expected rate for major abnormalities stands at 1 to 3 percent.

One new finding might provide a warning sign. Of the 125 exposed women, 75 had complained during pregnancy that organic chemicals were giving them headaches or breathing problems. Of the 13 major defects in the exposed group, 12 occurred in babies born to these women.

"We were quite amazed at the degree of effect we found," Khattak says.

The exposed women also had nine premature births, compared with three in the control group. This is the first study to measure premature births among women exposed to organic solvents, Khattak says.

Earlier tests in animals had shown that chemicals inhaled by pregnant rodents can cross the placental barrier to damage their young. Some studies of human mothers hinted that exposure to organic solvents might be to blame for birth defects, but others did not.

Because the Motherisk researchers identified the exposed women early in pregnancy, their work avoids the errors and biases of studies that later ask mothers to recall their exposures during pregnancy, says Richard K. Miller, an obstetrician and gynecologist at the University of Rochester (N.Y.) Medical Center.

"This paper from Motherisk is certainly the benchmark for examining the relationship between maternal toxic [exposure] and birth defects," he says. Its results will change how doctors counsel pregnant women regarding occupational risks, especially those that cause symptoms in the women, he predicts.