April 28 —, 2004 -- As if anyone needed another excuse not to go to the dentist, researchers now suggest pregnant women getting dental X-rays are more likely to have underweight babies.
Dentists already know not to take unnecessary X-rays of pregnant patients, since certain forms of radiation have been linked to pre-term labor and low-birth weight. But a new study is the first to link dental X-rays with low birth weight and full-term babies.
Study authors say they were surprised by the results, published in the Journal of the American Medical Association on Tuesday. Researchers previously assumed only direct radiation to the uterus or fetus would be harmful. The authors speculate the finding may have something to do with radiation effects on the thyroid gland or other hormonal systems in the head and neck region.
An examination of the records for more than 5,500 patients in the state of Washington showed pregnant women exposed to very low-dose radiation at the dentist's office, equivalent to a diagnostic X-ray series done for first-time patients, were twice as likely to have a low birth weight baby as those who didn't receive dental X-rays.
For full-term infants only, those born of mothers receiving dental X-rays during pregnancy were more than three times as likely to be of low birth weight.
Keep Your Appointments With the Dentist
Both the study authors and other experts agree the finding shouldn't discourage expectant mothers to cancel their dental appointments.
"The study certainly does show an association with X-rays, but this should not be mistaken to be a definite cause-and-effect situation," says Dr. Douglass Benn, professor of radiology and director of oral diagnostic systems at University of Florida College of Dentistry in Gainesville. Benn was not involved in the study.
The study's lead researcher, Dr. Philippe P. Hujoel, professor of dental public health sciences at University of Washington in Seattle, Wash., believes the study did a reasonable job of ruling out other possible causes for the association. But he acknowledges the need for future confirmation before the link can be solidified.
"It has been very difficult to study very low-dose radiation in pregnant women," Hujoel says. "Alternative explanations have not been ruled out yet."
Other Explanations for Low Birth Weight
Perhaps the most obvious alternative explanation is dental disease itself, specifically periodontal disease.
Studies have already linked periodontal and dental disease with pregnancy complications, especially pre-term labor and pre-term delivery. There is now speculation that dental disease can also lead to low birth weight for term infants.
"A patient who has periodontal disease has increased probability of pre-term labor or low birth weight," says Dr. Ira Lamster, dean of Columbia University School of Dental and Oral Surgery in New York.
But Hujoel says study data did not suggest periodontal disease as a possible cause. Besides, he says the link has not been well-established. In 2002, for instance, a British study of over 700 women in labor wards concluded periodontal disease was not associated with pre-term delivery and low birth weight, contradicting other earlier studies.
Other variables that could affect birth outcomes included maternal age, smoking, alcohol consumption, pregnancy weight gain, and maternal diseases — all of which Hujoel said the study took into account.
He notes, however, some women may have received additional X-rays for outside medical reasons, which he says could not have been controlled for in this study.
How to Minimize X-ray Exposure
Current guidelines from the American Dental Association instruct dentists to avoid taking X-rays on pregnant patients if at all possible, especially during the first trimester when fetal organs are developing, and the third trimester when the risk of inducing pre-term labor is higher.
Experts, including Hujoel, say this study shouldn't change those guidelines.
"It reiterates what we're already telling them," says Dr. Ken Burrell, senior director of the counsel on scientific affairs for the ADA in Chicago, Ill. He says unnecessary X-rays can be delayed until after pregnancy.
Burrell also stresses the importance of using lead aprons and neck collars to minimize radiation exposure, which he believes most dentists do. In addition, there should be open lines of communication.
"It would be worthwhile to inform the dentist if you are pregnant," says Hujoel. Since many of women in the study had their dental X-rays during the first trimester, he speculates they either didn't know they were pregnant, never thought to tell their dentists, or their dentists never bothered to ask.
"Pregnant women should not skip their dental visits," emphasizes Dr. Marjorie Jeffcoat, dean of University of Pennsylvania School of Dental Medicine in Philadelphia. She says if you have symptoms or an infection, going to the dentist is still the best thing to do for both your unborn child and yourself, even if treatment requires X-rays to be taken.
Benn warns allowing tooth or gum disease to fester can lead to a more severe infection that can reach the fetus through the blood. Treatment would then require taking X-rays anyway, and could warrant more extensive treatment requiring anesthesia and oral surgery, putting the fetus at even higher risk for harm.