Imaging in Pregnancy (part I)

Ionizing Radiation (Xray and CT)

The fetus is most susceptible to the teratogenic effects of ionizing radiation, which include microcephaly, mental retardation, growth restriction, and cataracts. This is likely based on the embryonic age: 2-8 weeks skeletal/growth restriction/cataracts, 8-20 weeks microcephaly/mental retardation. The threshold radiation dose to cause teratogenic effects is estimated to be between 0.05–0.15 Gy (5-15 rad). The relative risk of cancer after exposure to 0.05 Gy (5 rads) is 2. The American College of Obstetricians and Gynecologists (ACOG) does not provide risk estimates due to radiation exposure but described it as “very small” and conclude that “abortion should not be recommended.” Interestingly, during the course of pregnancy background radiation dose is around 1 Gy.

Intravenous contrast is category B and intravascular use of nonionic contrast media has been reported to have no effect on neonatal thyroid function.

Common imaging and radiation doses:

• abdominal radiograph 0.001–0.003 Gy (0.1–0.3 rads)
• intravenous pyelogram 0.006 Gy (0.6 rads)
• barium enema 0.007 Gy (0.7 rads)
• lumbar spine radiograph 0.006 Gy (0.6 rads)
• CT pelvis 0.02–0.05 Gy (1–5 rads)

MRI

The U.S. Food and Drug Administration indicate that the safety of MRI with respect to the fetus “has not been established.” Most studies evaluating MRI safety during pregnancy show no ill effects. From animal data showing teratogenic effects secondary to MRI the National Radiological Protection Board in the United Kingdom has recommended that “it might be prudent to exclude pregnant women during the first three months of pregnancy.”

Gadolinium is classified as a category C. The American College of Radiology recommends that intravenous gadolinium should be avoided during pregnancy and should be used only if absolutely essential. Growth retardation and congenital anomalies have been observed  when administered to animals at doses two to seven times higher than those used in humans.

In part II the recommended imaging for selected situations will be discussed.

Patel SJ, Reede DL, Katz DS, Subramaniam R, Amorosa JK. Imaging the pregnant patient for nonobstetric conditions: algorithms and radiation dose considerations.Radiographics. 2007 Nov-Dec;27(6):1705-22.

Chen MM, Coakley FV, Kaimal A, Laros RK Jr. Guidelines for computed tomography and magnetic resonance imaging use during pregnancy and lactation. Obstet Gynecol. 2008 Aug;112(2 Pt 1):333-40.