Dental X-Rays Linked to Underweight Babies

Dental X-rays during pregnancy can significantly impair the health of a fetus even though it does not receive radiation directly, according to researchers at the University of Washington.

Pregnant women exposed to dental radiation were nearly four times as likely to have a baby with a low birth weight, even though their pregnancies were full term, the team reports today in the Journal of the American Medical Assn.

Low birth weights have been linked to developmental and behavioral problems in infants.

Direct exposure of a fetus to radiation is known to be harmful, but lead aprons and directional X-rays have virtually eliminated direct exposure during dental procedures.

The researchers concluded that 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 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 experts have blamed periodontal disease, mercury amalgam fillings and composite fillings.

Hujoel said his group wanted to determine how big a role each of those factors played.

The link to radiation “popped out very strongly,” he said.

The team found no connections to the other factors.

The researchers used data from Washington Dental Service, a nonprofit dental insurance company, and Washington state birth records.

They identified 1,117 low birth-weight infants born from January 1993 to December 2000 and matched them with 4,468 children of normal weight born during the same period.

They found that about 10% of pregnant women had undergone dental procedures, and that those who had X-rays were 3.6 times as likely to deliver a baby with a low birth weight 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 resampled the population and went through a lot of steps to convince ourselves that this association was present.”

Hujoel was not sure how radiation produces its effects.

But Hujoel speculated that it could create a small thyroid or other hormonal dysfunction in a pregnant woman, which may in turn affect the fetus’ ability to thrive.

The group hopes to follow up by measuring hormone levels in affected women to determine if that is the case.