Living Near Where Pesticides Used May Boost Fetal Death Due To Birth Defects

"Our study showed a consistent pattern with respect to timing of exposure," said Dr. Erin M. Bell, who earned her doctorate with the research at the UNC School of Public Health. "The largest risks for fetal death due to birth defects were from pesticide exposure during the third week to the eighth week of pregnancy."

That span -- much of the first trimester -- appears to be a special window of vulnerability for birth defects, Bell said, just as earlier research has suggested.

"The risks appeared to be strongest among pregnant women who lived in the same square mile where pesticides were used," she said.

A report on the research will appear in the March issue of Epidemiology, a public health journal. Besides Bell, now an epidemiologist with the National Cancer Institute, authors were her mentor Dr. Irva Hertz-Picciotto, professor of epidemiology at UNC, and Dr. James J. Beaumont, formerly of the University of California at Davis and now with the California Environmental Protection Agency.

"This is the first study to our knowledge of pesticides and pregnancy in which exposures were in close proximity to the subjects and the verification of pesticide use was objective, not relying on people's memories of what they might have been exposed to," Hertz-Picciotto said.

Researchers tapped information about dates, locations and amounts of chemicals applied by air or ground equipment resulting from the California law requiring that all restricted pesticide use be reported. They compared that with detailed information about where pregnant women lived and what happened with their pregnancies.

"The take-home message is that we did find an increased risk for women living near agricultural fields where pesticides were applied during the early weeks of their pregnancies, but these results are not conclusive," Bell said.

Investigators cautioned that further study is needed since they lacked certain information.

"Our exposure classification method did not guarantee that a mother was in fact exposed because wind and weather conditions, hour of application and the location of the mother at the times of application were all factors that would determine actual exposure," she said.

Women considering becoming pregnant who are worried about pesticide exposure should consult their physicians, she said. Five pesticide classes were examined in the new study. Those were phosphates, pyrethroids, halogenated hydrocarbons, carbamates and endocrine disruptors.

About 19,000 fetal deaths occur in the United States each year, and the causes remain a significant public health problem, Bell said. Among known risk factors are smoking, advanced age among pregnant women and previous history of fetal deaths.

In the past, few epidemiological studies of pesticide exposure and birth defects have considered timing of possible exposures. California counties included in the new UNC study were Madera, Tulare, Kings, Merced, Monterey, Stanislaus, San Joaquin, Riverside, Fresno and Kern.