Dental X-Rays Associated With Increased Risk of Low Birth Weight Babies
Low birth weight is defined as less than 5 pounds, 8 ounces (2,500 grams) at birth. Although advancements in newborn medical care have greatly reduced the number of low birth weight babies who die every year, many still face serious health problems and are at increased risk of long-term disabilities.
Radiation’s relationship to low birth weight babies is clear. Past research has shown that young girls who received high dose radiation treatment for childhood cancers are at risk for low birth weight babies later in life. The same is true for adolescent girls and pregnant women who receive medical radiation; depending on the amount of radiation they receive and the areas of exposure in the body.
What researchers don’t know is whether the relationship between radiation and low birth weight is the result of its direct action on the reproductive organs or its effect on the endocrine system, specifically the hypothalamus, pituitary, and thyroid glands, all of which are involved in pregnancy.
To answer this question, a group of researchers set out to determine the effects of dental x-rays on pregnant women. The results of their study were published in the April 28, 2004 issue of The Journal of the American Medical Association. They found that exposure to certain doses of radiation through dental x-rays increased a woman’s risk of having a low birth weight baby.
About the Study
The researchers examined the dental records for all women between the ages of 12 and 45 who were treated at a dental center between January 1993 and December 2000. They then linked these records to birth certificates. In the end, the researchers identified 1,117 women who had low birth weight babies and 4,468 women who had normal birth weight babies.
The researchers estimated the amount of radiation each woman in the study was exposed to according to the type of x-rays she received. For example, a full mouth x-ray had an estimated radiation dose of 1.6 milligray (mGy) while a series of four “bitewing” x-rays had an estimated dose of only 0.22 mGy. For the purposes of the study, the researchers broke the women into three categories of total radiation exposure:
- 0 mGy (no dental x-rays)
- 0.1-0.4 mGy
- more than 0.4 mGy
The researchers found that among women who had low birth weight babies, 1.9% had received total radiation doses greater than 0.4 mGy. Among women who gave birth to normal weight babies, only 1.0% had received an equally high dosage of radiation. Women who gave birth to low birth weight, full-term (37 or more weeks of pregnancy) babies had also received higher radiation doses than woman who gave birth to normal weight full-term infants. Indeed, the strongest association between dental x-rays and low birth weight was among this group of babies.
How Does This Affect You?
The researchers concluded that dental x-rays in pregnant women were associated with an increased risk of low birth weight babies, particularly when those babies were carried full term.
The researchers acknowledge that because many women, at least in the early stages, are often unaware of their pregnancy status it may not be possible to eliminate exposure to dental x-rays from every pregnancy. However, keeping in mind that approximately 10% of the women in the study population received some type of dental x-ray during the course of their pregnancy, taking steps to avoid this type of exposure could reduce the total number of full-term low birth weight babies by as much as 5%, according to the researchers.
However, this study has a number of important limitations, including its design. Case control studies, like this one, compare participants who have a certain condition with participants who do not. Even if this comparison demonstrates a statistical relationship, it does not necessarily demonstrate a causal one. For example, if a study finds that lung cancer rates are higher for people without a college education (who tend to smoke more), it does not mean you can reduce your risk for lung cancer simply by getting a college education.
Therefore, while this study shows a relationship between low birth weight babies and exposure to dental x-rays, it does not mean that dental x-rays cause low birth weight babies. A study that follows women over time, and carefully controls for confounding factors, would give us a better understanding of the causative role of dental x-rays in low-birth weight pregnancies. Nevertheless, it certainly seems reasonable to avoid dental x-rays if you are pregnant or trying to become pregnant, unless absolutely necessary.
Centers for Disease Control and Prevention.
Hujoel PP, Bollen AM, Noonan CJ, et al. Antepartum dental radiography and infant low birth weight. JAMA. 2004;291:1987-1993.
Low birthweight. March of Dimes. Available at: http://www.modimes.org/professionals/681_1153.asp . Accessed April 28, 2004.
Last reviewed April 30, 2004 by ]]>Richard Glickman-Simon, MD]]>
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