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Study: Dental X-Rays During Pregnancy Tied to Low Birth Weight Babies - 2004-04-28

A new study indicates that dental x-rays during pregnancy are associated with low birth weight babies. The finding could have an impact on current medical guidelines, which call for pregnant women to avoid only x-rays of reproductive organs.

Dental x-rays might be harmful to a pregnant woman's unborn child. This is the finding of a study in the Journal of the American Medical Association led by University of Washington researcher Philippe Hujoel.

"We found an association between very low dose head and neck radiation and low birth weight. Many people will be surprised that we see an association at such a low dose," he said.

Mr. Hujoel and colleagues studied the birth outcomes of 4,500 pregnant women in the northwestern U.S. state of Washington between 1993 and 2000. The mothers delivered about 1,100 low birth weight babies, each less than 2.5 kilograms. Women who had dental x-rays had about twice the risk of delivering an underweight premature baby and three times the risk of a low-weight full term baby. The risk increased with greater doses of radiation.

Previous studies have found that women face a similar risk if they were exposed to high dose radiation for cancer or other conditions around the age of adolescence. This is also true of pregnant mothers who get medical radiation. As a result, pregnant woman are advised to avoid medical x-rays. But Mr. Hujoel says there are no guidelines for lower dose dental x-rays.

"Currently the guidelines say that women who are pregnant are eligible for receiving very low dose diagnostic radiation to the head and neck, because up until now people assumed that head and neck radiation will not have any adverse effects on pregnancy outcomes. They assumed that only direct radiation to the uterus or the fetus would be associated with adverse pregnancy outcomes," he said.

The researchers are not sure why a mother's dental x-rays might affect a fetus. They speculate that the procedure could have impact on the production of hormones by the thyroid gland in the mother's neck. Some studies have found that women with mild thyroid disease have an increased chance of underweight newborns.