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April 27, 2004 — Pregnant women who are exposed to dental radiography may be more likely to give birth to an infant who weighs less than normal, according to a study in the April 28 issue of The Journal of the American Medical Association.
According to background information in the article, the link between radiation and low birth weight (LBW) babies has been established with medical X-rays, but not dental X-ray radiation. "Because dental diagnostic radiography results in measurable radiation doses to the hypothalamus-pituitary-thyroid axis and not the reproductive organs or the fetus, it provides an opportunity to test the role of the hypothalamus-pituitary-thyroid axis in the radiation-LBW association," the authors write.
Philippe P. Hujoel, Ph.D., and colleagues from the University of Washington, Seattle, analyzed data from Washington Dental Services, a non-profit dental insurance company in Washington State, for women who received dental treatment between January 1993 and December 2000. Those records were then linked to birth certificates. There were 1,117 low birth weight infants (defined as weighing less than 2,500 grams or 5.5 pounds) born to women with Washington Dental Service insurance during that time period. A total of 4,468 normal birth weight (NBW) infants were selected as the control group for this study.
The investigators estimated the amount of radiation exposure based on the dental X-ray studies performed and published radiation dosages. (For example, a full mouth 21 X-ray series has a typical dose of 1.6 mGy [milligray] of radiation, whereas a series of four "bitewing" X-rays has a dose of 0.22 mGy). For their analysis, the authors categorized the cumulative radiation exposure into three dose groups: 0 mGy (no dental x-rays), 0.1-0.4 mGy, and higher than 0.4 mGy (which corresponded to the 90th percentile of the cumulative radiation doses among women who had at least one dental X-ray.)
Among the women who delivered a LBW infant, 1.9 percent (n = 21, including 10 LBW infants born at term) had higher than 0.4 mGy radiation dose, compared with 1.0 percent of women with NBW infants. When compared to women with no known dental diagnostic X-rays during pregnancy, a radiation dose of more than 0.4 mGy was associated with an increased adjusted odds for LBW of 2.27, and an increased adjusted odds for term LBW of 3.61.
"In this study, antepartum (before birth) dental radiography in pregnant women was associated with an increased risk for a LBW infant, especially a TLBW (term low birth weight) infant. The prevalence of dental radiography during pregnancy in this dentally insured population was approximately 10 percent. Since women may not always be aware of their pregnancy status, it may not be possible to eliminate all dental radiography during pregnancy, but if this goal could be achieved and if the identified association is causal, the prevalence of TLBW infants could be reduced by up to 5 percent," the authors suggest. In conclusion the authors write: "The notion that very low-dose radiation exposures to nonreproductive organs in expectant mothers are safe needs to be investigated further."