Dental X-rays taken during pregnancy can significantly impair the health of the fetus even though it does not receive radiation directly, according to a study by researchers from the University of Washington.
Pregnant women who were exposed to dental irradiation were nearly four times as likely to have a low birth weight baby, though their pregnancies went full term, the team reports today in the Journal of the American Medical Association.
Low birth weights have been widely associated with developmental and behavioral problems in infants.
Direct exposure of a fetus to radiation is known to have a variety of adverse effects, but the use of lead aprons and directional X-rays has virtually eliminated such direct exposure during dental procedures. So the X-rays must be exerting an indirect effect on fetal development through the mother.
"Women should try to avoid elective dental radiographs or any others during pregnancy, especially during the first trimester," said Dr. Philippe P. Hujoel, who led the study.
Researchers have long known of an association between dental procedures during pregnancy and low birth weights, but the nature of the link has not been clear. Some have attributed the effect to periodontal disease, some to mercury amalgam fillings, and some to composite fillings.
Hujoel said his group undertook the study in an effort to determine how big a role was played by each of those factors. The link to radiation "popped out very strongly," he said.
Although it is not reported in the current paper, he added, the team found no links to any of the other factors.
The team used data from Washington Dental Service, a not-for-profit dental insurance company, and Washington State birth records. They identified 1,117 low birth weight infants born between January 1993 and December 2000 and matched them with 4,468 children of normal weight born during the same period.
They found that about 10 percent of pregnant women had undergone dental procedures, and that those who had X-rays were 3.6 times as likely to deliver a low birth weight baby as those who were not exposed to radiation.
The results were "very surprising ... because the amount of radiation pregnant women were exposed to was very low and generally thought to be incapable of inducing observable health effects," Hujoel said. "We went back and re-sampled the population and went through a lot of steps to convince ourselves that this association was present."
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