Medical imaging in pregnancy

For the first trimester, no known literature has documented specific adverse effects in human embryos or fetuses exposed to non-contrast MRI during the first trimester.[3] During the second and third trimesters, there is some evidence to support the absence of risk, including a retrospective study of 1737 prenatally exposed children, showing no significant difference in hearing, motor skills, or functional measures after a mean follow-up time of 2 years.[3]

Gadolinium contrast agents in the first trimester are associated with a slightly increased risk of a childhood diagnosis of several forms of rheumatism, inflammatory disorders, or infiltrative skin conditions, according to a retrospective study including 397 infants prenatally exposed to gadolinium contrast.[3] In the second and third trimesters, gadolinium contrast is associated with a slightly increased risk of stillbirth or neonatal death, by the same study.[3] Hence, is recommended that gadolinium contrast in MRI should be limited, and should only be used when it significantly improves diagnostic performance and is expected to improve fetal or maternal outcomes.[1]

MRI is commonly used in pregnant women with acute abdominal pain and/or pelvic pain, or in suspected neurological disorders, placental diseases, tumors, infections, and/or cardiovascular diseases.[3] Appropriate use criteria by the American College of Radiology give a rating of ≥7 (usually appropriate) for non-contrast MRI for the following conditions:

• Acute non-localized pain in the right upper quadrant or right lower quadrant (in concurrent fever and leukocytosis)[3]
• Acute pelvic pain when a non-gynecological cause is suspected[3]
• Suspected biliary disease such as jaundice[3]
• Suspected pancreatic disease[3]
• New‐onset severe headache[3]
• Newly diagnosed cancer[3]

Health effects of radiation may be grouped in two general categories:

• stochastic effects, i.e., radiation-induced cancer and heritable effects involving either cancer development in exposed individuals owing to mutation of somatic cells or heritable disease in their offspring owing to mutation of reproductive (germ) cells.[4] The risk for developing radiation-induced cancer at some point in life is greater when exposing a fetus than an adult, both because the cells are more vulnerable when they are growing, and because there is much longer lifespan after the dose to develop cancer.
• deterministic effects (harmful tissue reactions) due in large part to the killing/ malfunction of cells following high doses.

The determinstistic effects have been studied at for example survivors of the atomic bombings of Hiroshima and Nagasaki and cases of where radiation therapy has been necessary during pregnancy:

The intellectual deficit has been estimated to be about 25 IQ-points per 1,000 mGy at 10 to 17 weeks of gestational age.[1]

The risk for the mother of later acquiring radiation-induced breast cancer seems to be particularly high for radiation doses during pregnancy.[5]

This is an important factor when for example determining whether a ventilation/perfusion scan (V/Q scan) or a CT pulmonary angiogram (CTPA) is the optimal investigation in pregnant women with suspected pulmonary embolism. A V/Q scan confers a higher radiation dose to the fetus, while a CTPA confers a much higher radiation dose to the mother's breasts. A review from the United Kingdom in 2005 considered CTPA to be generally preferable in suspected pulmonary embolism in pregnancy because of higher sensitivity and specificity as well as a relatively modest cost.[6]