Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, July 7, 1994 TAG: 9407070144
SECTION: NATIONAL/INTERNATIONAL PAGE: A1 EDITION: METRO
SOURCE: Associated Press
DATELINE: LENGTH: Medium
BOSTON - A study of more than 370,000 mothers provides some of the strongest evidence yet that where people live and work powerfully affects the risk of birth defects.
The study, conducted in Norway, followed women who gave birth to a defective child. Not surprisingly, it found that they face a high risk of having a second child with the same birth defect.
However, the study also discovered that the risk is cut in half if the mother moves to another town. This suggests some environmental factors are at work in triggering birth defects and are more important than experts had suspected.
``It's surprising that we see evidence of environmental effects in the data we looked at. It suggests there are things out there that we just have not been clever or lucky enough to find so far,'' said Dr. Allen J. Wilcox, a co-author of the study.
Wilcox, a researcher at the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., said the study could not identify the precise environmental hazards that contribute to birth defects.
More than 150,000 babies are born with serious birth defects in the United States each year. In about two-thirds of the cases, the causes of the defects are a mystery.
Most of the known causes of birth defects are specific genetic mutations. Other causes include alcohol abuse, poor diets and some medicines and chemicals, such as mercury.
However, experts long have suspected that genetic tendencies and environmental hazards are involved in many more cases. One leading theory holds that some unidentified environmental substances are harmless to most people but can trigger birth defects in those who have a genetic susceptibility.
``This clearly leads us to conclusions about the importance of environmental factors,'' said Kay Johnson, policy director at the March of Dimes.
The study was directed by Dr. Rolv Terje Lie of the University of Bergen in Norway and published in today's issue of the New England Journal of Medicine. It was based on the records of first and second infants delivered by 371,933 women from 1967 through 1989.
For the 9,192 women whose first babies had a birth defect, the researchers determined the risk of defects in the second baby. This was compared with the risk in women whose first babies were normal. Overall, 2.5 percent of the first babies had birth defects.
Among the findings:
nWomen who had given birth to one defective baby faced nearly seven times the usual risk of having a second child with the same defect.
nAmong those who continued to live in the same town, the risk of a second baby with the same defect was 12 times higher than usual. But if they moved, it fell to five times higher.
nWomen whose first baby had a cleft lip were 31 times more likely than other women to have a second baby with the defect. The increased risk for a second baby with limb defects was 11 times; clubfoot, seven times; and genital defects, five.
The study ``implies that there may be some agents out there that large numbers of people are exposed to - and maybe not in terribly high doses - that may have an effect on reproductive outcomes,'' commented Dr. James Hanson, director of the University of Iowa's Institute for Health, Behavior and Environmental Policy.
The study was based on the Medical Birth Registry of Norway, which includes about 1.5 million birth records.
nWhen these women changed partners after their first defective child, their risk of having a second baby with a defect appeared to fall, but the change was not statistically meaningful.
nA woman who had one baby with a birth defect faced about a 4 percent chance of having a second child with some kind of serious defect.
``Moving changes a lot of things in your life,'' he said. ``But it suggests there may be certain factors linked to the household or related to a job change. It can only give us the barest kinds of leads.''
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