Ionizing radiation has also been linked to an increased risk of malignancy. The data used to make this link has been extrapolated from the cancer rates following atomic bomb exposure in Hiroshima and Nagasaki, as well as the aftereffects of the Chernobyl disaster. Cumulative exposure to 100 mGy of ionizing radiation is associated with increased risk of developing malignancy; below this level, cancer cannot be correlated with radiation exposure. Diagnostic medical tests involving ionizing radiation utilize significantly less radiation than 100 mGy.

The American College of Obstetricians and Gynecologists (ACOG) supports the use of medical diagnostic imaging when the radiation exposure is less than 50 mGy, as fetal anomalies have not been reported below this level [2]. However, the use of ionizing radiation studies should not be withheld in a pregnant patient regardless of the radiation dose if there is an emergent clinical indication. Appropriate and timely diagnosis and treatment of the emergency affecting the mother is the safest way to protect the fetus.

X-ray is the most common form of ionizing radiation used during pregnancy. Most X-rays are very low-dose examinations (<0.1 mGy) and therefore pose almost no risk to the fetus. Very low-dose X-rays include the cervical spine, chest (two views), and any extremity films. Low- to moderate-dose examinations (0–10 mGy) include abdominal, thoracic, and lumbar spine X-rays (Table 13.2. Fetal radiation doses).

The highest doses of ionizing radiation are from CT scans. For example, a CT angiography of the chest to rule out pulmonary embolism exposes the mother to anywhere between 13 and 40 mGy of radiation with the average being about 15 mGy depending on the radiology protocol and type of machinery [6]. The fetal exposure is much less, between 0.01 and 0.66 mGy. A CT of the abdomen and pelvis during pregnancy exposes a fetus to approximately 25 mGy. CT of the head, neck, and extremities usually results in only negligible scatter radiation to the fetus [6].