Dental X-rays may harm unborn babies

Pregnant women who have dental X-rays may increase their risk of giving birth to babies with a low birth weight, a new study says.

University of Washington researchers found that these women had almost double the risk of having an underweight baby born prematurely and more than triple the risk of having a full-term baby of low birth weight. The study was published in this week’s Journal of the American Medical Association.

A low-birth-weight baby weighs less than 5 pounds, 3 ounces at birth.

“The amount of radiation in a dental X-ray is so low, it’s hard to imagine it could have [adverse] medical consequences, but the results of this study show there should be further follow-up research” in this area, Dr. Philippe Hujoel, the study’s lead author, said yesterday.

Dr. Michael Fleming, president of the American Academy of Family Physicians (AAFP), called the findings “a surprise” and agreed more research is needed.

He said the AAFP has long held that medical and dental X-rays are safe for pregnant women.

“That’s because all the data that was available indicated they were safe,” he said.

“This research was very well done and very credible. But there will need to be corroboration,” he said, adding, “This deserves significant study.”

The study involved about 4,500 women who gave birth while enrolled in a dental-insurance plan in Washington state between 1993 and 2000.

A total of 1,117 low-weight babies were born to study participants. Twenty-one of those infants were born to women who had dental X-rays, all in the first trimester of pregnancy. No link was found between X-rays and the smallest babies in the study.

Asked why so few of the underweight infants were linked to dental X-rays, Dr. Hujoel said dentists “try to avoid” exposing pregnant women to radiation, especially during the first trimester.

As for how the X-rays might affect a baby’s size, Dr. Hujoel speculated that radiation may cause subtle changes in the functioning of a mother’s thyroid gland. He said previous research found an increased risk of low-birth-weight babies in women with mild thyroid disease.

Dr. Sally Cram, a periodontist in the District and a spokeswoman for the American Dental Association (ADA), said the association advises dentists to avoid giving women X-rays during the first four months of pregnancy, if possible.

“The second trimester seems to be a safer period,” she said.

As for the study in JAMA, Dr. Cram said, “It points out a possible relationship between dental X-rays and low-birth-weight babies. But it only suggests a statistical association at this point. Many other variables were not ruled out, so this was not a cause-and-effect article.”

Dr. Hujoel and Dr. Cram agree that pregnant women in need of emergency dental care should not forgo it, even if it involves X-rays. Dr. Cram also said all patients should be given protective collars and aprons that cover the neck and upper body.