Frush considers MSCT safe for pregnant women, fetuses despite radiation exposure

May 19, 2009

Radiation exposure from multislice CT may be a reason for concern regarding pregnant women and fetuses, but Dr. Donald P. Frush does not consider it a contraindication to performing medically necessary procedures.

Radiation exposure from multislice CT may be a reason for concern regarding pregnant women and fetuses, but Dr. Donald P. Frush does not consider it a contraindication to performing medically necessary procedures.

The Duke University professor of pediatric medicine advised an audience at the International Symposium on Multidetector-Row CT Tuesday that care should be taken to inform the mother how much ionizing radiation is involved during CT imaging. But the radiologist should stress that the resulting risks of miscarriage, cancer, or death are too small for measurement, he said.

"CT is a source of great anxiety for all of those involved, and a source of misunderstanding," Frush said.

The anxiety stems from CT's swift growth as the imaging modality of choice for some diagnostic procedures performed on pregnant women. The misunderstanding arises from the media, such as a fall 2008 report in the Los Angeles Times suggesting that CT caused a Los Angeles-area woman to miscarry.

"This is bad journalism," Frush said. "There are no scientific data that establish a single CT scan or -- two CT scans even -- will result in an increased risk of miscarriage."

Yet even the medical community has been highly suspicious of CT and the effects of radiation on fetal health, Frush said. A 2003 survey, for example, found that 4% of physicians recommended abortion for women in need of a single CT exam. Another 25% said they were uncertain about the relationship between the radiation from a single CT scan and the need for abortion.

In reality, a 1 to 10-milligray fetal dose should be considered to carry negligible risk for most x-ray, fluoroscopic, and nuclear imaging techniques involving ionizing radiation, Frush said.

A single CT scan whose field-of-view is focused outside the uterus will involve negligible dose to the fetus as well. Scans directed at the uterus and fetus will involve 25 to 50 mGy, he said.

Even scans involving much more radiation (100 to 500 mGy) will still involve zero risk for miscarriage, heritable defects, fetal malformations, or central nervous system damage. The future risk of cancer is considered small, Frush said.

With this in mind, a pregnant woman can be reassured that the risks of a single CT scan will be negligible, he said. Rather than focusing on risk, Frush advised radiologists to concentrate on the probability of delivering a normal child after CT. The likelihood of normal delivery is 97% for exposures up to 50 mGy. The probability of the child being cancer-free through the first 20 years of life is 99.4%. Radiation ranks low on the list of reasons for problem pregnancies, he said.

Still, an internal policy concerning the use of CT on pregnant women is essential for hospitals and clinics, he said. Risk management personnel, legal counsel, medical physicists, obstetricians, and emergency care physicians should participate with radiologists in forming such a policy, he said. Medical considerations include the institution's imaging algorithms, its use of dose reduction strategies, and policies for offering alternative imaging modalities to pregnant women. The need for informed consent depends on the hospital's specific situation. Case documentation is essential.

The actual risks at any given institution must be understood, however.

"Otherwise, it is very difficult to try to explain these things to a pregnant woman who is about to undergo a CT examination," he said.