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TUESDAY, April 27 (HealthDayNews) -- Getting dental X-rays during pregnancy could result in smaller-than-normal babies.

If it were possible to eliminate all dental X-rays during pregnancies, the prevalence of small babies might be reduced by up to 5 percent, say the authors of a study appearing in the April 28 issue of the Journal of the American Medical Association.

Although the association between the two needs to be investigated further, experts are advising women who are planning to have a baby to visit their dentist before actually conceiving.

"We've been doing things for many years to protect our patients against excessive radiation," said Dr. Sally Cram, consumer advisor for the American Dental Association and a practicing periodontist in Washington, D.C. "But women who are considering getting pregnant or who are pregnant should certainly take very seriously their oral health so as to avoid having emergency X-rays that could potentially cause harm to the fetus or the child."

It has long been known that radiation from medical X-rays could cause problems with pregnancy, but the picture with dental X-rays has not been so clear. Unlike medical X-rays, dental X-rays do not deliver radiation directly to the reproductive organs or the growing fetus, but to the area of the upper body containing the hypothalamus and pituitary and thyroid glands. Any effect on pregnancy would be indirect through those areas.

The study authors looked at records from Washington Dental Services, a nonprofit dental insurance company in Washington State. Data on women who had received dental treatment between January 1993 and December 2000 were cross-referenced with birth certificates. Only single births were included in the study.

During that time, 1,117 low birth weight infants (weighing less than 5.5 pounds) were born. The authors estimated the amount of radiation each mother had received from dental X-rays, then compared that to the amount of radiation mothers of 4,468 normal birth weight infants had received.

Among the women who had had a small birth weight baby, 1.9 percent had had a higher than 0.4 milligray (mGy) radiation dose. Only 1 percent of women with normal-size babies had received that high a dose.

Compared with women who had had no dental X-rays during pregnancy, women who received more than 0.4 mGy had an overall 2.27 higher chance of having a small baby. Those whose pregnancies went to full term, however, had a 3.61 higher chance of having a small baby.

It's not clear from this study which gland may be responsible for the change although, as the study authors pointed out, low-dose radiation has been associated with thyroid problems. Nevertheless, current guidelines may need to be revised, as they focus only on direct radiation to the reproductive organs, the authors stated.

The American Dental Association recommends that elective dental X-rays be postponed until after the baby has arrived. If X-rays are needed, they recommend protective aprons for the abdomen as well as "thyroid collars" to minimize exposure to radiation. Women should also tell their dentists if they are pregnant, might be pregnant or are planning to become pregnant.

"Women should have regular dental check-ups and cleanings before pregnancy to ensure that they're not in a situation where you need emergency care," Cram emphasized.

The March of Dimes also advises leaving invasive procedures and X-rays until after the pregnancy. "Women who are currently pregnant should make sure they inform their dentist and, if it's not absolutely necessary that these X-rays be done, they should wait," said Dr. Diane Ashton, associate medical director of the March of Dimes.

More information

The American Dental Association has more on oral health and pregnancy. The March of Dimes has more on prematurity.

(SOURCES: Sally Cram, D.D.S., consumer advisor, American Dental Association, Washington, D.C.; Diane Ashton, M.D., associate medical director, March of Dimes, White Plains, N.Y.; April 28, 2004, Journal of the American Medical Association)

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