Report from NCRP: Radiation exposure during pregnancy demands well-informed patient management

Thousands of pregnant women are exposed to ionizing radiation every year in the U.S., as either patients or healthcare workers who use equipment as it generates ionizing radiation. Their ignorance about the true implications of radiation exposure during pregnancy is a source of great anxiety and may lead to a decision to abort in some instances, said Dr. Claire Cousins, chair of the International Commission on Radiological Protection's medical subcommittee.

Cousins spoke at the 2007 National Council on Radiation Protection and Measurements meeting.

Radiation exposure may endanger the radiosensitive fetus, but the level of risk depends on the stage of pregnancy and absorbed dose, she said. As documented in ICRP Publication 84 on pregnancy and medical radiation, the risk is highest during organogenesis, a period from two to seven weeks after conception. It is somewhat less dangerous during the second trimester and even less dangerous in the third.

Fetal doses below 100 mGy, the equivalent to about three pelvic CT scans or 20 x-ray exams, are generally safe and do not justify termination of pregnancy. But doses in excess of 100 mGy may produce fetal damage, Cousins said.

Medical necessity is the most important factor determining if the benefits of radiation exposure during pregnancy outweigh the risks, Cousins said. Imagers should consider if an imaging exam involving exposure may be delayed until after childbirth. When imaging is essential, the physician should consider safe alternatives such as MRI and diagnostic ultrasound.

Pregnant physicians, technologists, and nurses should be temporarily reassigned to duties that keep them away from ionizing radiation sources, she said.

Some indications for x-ray, CT, or nuclear studies outweigh the health risk to the fetus. Diagnostic imaging poses relatively less risk than fluoroscopically guided interventional or radiotherapy procedures. Physicians need to balance the benefit to the mother versus the risk to the fetus without delaying a warranted indication, said Cousins, who is also an interventional radiologist at the Addenbrooke's Hospital in Cambridge, U.K.

"A pregnant patient should not be denied treatment to protect the fetus," she said.

Honest communications initiated by the physician and informed consent secured from the patient are important. Pregnant patients and their families should be informed about the magnitude and type of potential radiation effects that may result from in utero exposure. Patients receiving doses less than 1 mGy will appreciate knowing the effects are considered negligible. Physicians should explain in further detail the risks involved when the dose is higher than 1 mGy, Cousins said.

The RSNA has published a chart comparing the effective radiation dose for various CT and x-ray procedures and background radiation.

Women should inform their employers when they become pregnant to assure proper guidance regarding risks in their work environment. The NCRP recommends a dose limit of 0.5 mSv per month of pregnancy and 5 mSv for the entire gestational period.

Special section: Exclusive coverage of the 2007 National Council on Radiation Protection and Measurements meeting

This year's historic NCRP meeting reveals the disturbing growth of patient exposure to ionizing radiation from medical imaging and proposes practical solutions to regulate its growth. Extended coverage from Diagnostic Imaging lays out the facts and recommendations to better protect patients, physicians, and medical staff.

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