Medical imaging in pregnancy may beindicated because ofpregnancy complications,intercurrent diseases or routineprenatal care.

Options formedical imaging inpregnancy include the following:

• Magnetic resonance imaging (MRI) withoutMRI contrast agents as well asobstetric ultrasonography are not associated with any risk for the mother or the fetus and are the imaging techniques of choice for pregnant women.^[1]
• Projectional radiography,X-ray computed tomography andnuclear medicine result in some degree ofionizing radiation exposure but have with a few exceptions much lowerradiation doses than what is associated with fetal harm.^[1] They are indicated when ultrasonography or MRI is not readily available or not feasible for the diagnostic question at hand.^[1]

• Radiocontrast agents, whenorally administered, are harmless.^[1]Intravenous administration of iodinated radiocontrast agents can cross theplacenta and enter thefetal circulation, but animal studies have reported noteratogenic ormutagenic effects from its use. There have been theoretical concerns about the potential harm of free iodide on the fetalthyroid gland,^[1] but multiple studies have shown that a single dose of intravenously administered iodinated contrast medium to a pregnant mother has no effect on neonatal thyroid function.^[2] Nevertheless, it generally is recommended that radiocontrast only be used if required to obtain additional diagnostic information that will improve the care of the fetus or mother.^[1]

Magnetic resonance imaging (MRI), withoutMRI contrast agents, is not associated with any risk for the mother or the fetus, and together withmedical ultrasonography, it is the technique of choice for medical imaging in pregnancy.^[1]

For the first trimester, no known literature has documented specific adverse effects inhuman embryos or fetuses exposed to non-contrast MRI during thefirst 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 ofrheumatism,inflammatory disorders, or infiltrativeskin 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]

Women have a legal right to not be forced to undergo medical imaging without first providing informed consent; a radiologist is usually the healthcare provider trained to enable informed consent.^[4]

MRI is commonly used in pregnant women with acuteabdominal pain and/orpelvic pain, or in suspectedneurological disorders,placental diseases,tumors,infections, and/orcardiovascular diseases.^[3]Appropriate use criteria by theAmerican 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 andleukocytosis)^[3]
• Acutepelvic pain when a non-gynecological cause is suspected^[3]
• Suspectedbiliary disease such asjaundice^[3]
• Suspectedpancreatic disease^[3]
• New‐onset severeheadache^[3]
• Newly diagnosedcancer^[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.^[5] 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 theatomic bombings of Hiroshima and Nagasaki and cases of whereradiation therapy has been necessary during pregnancy:

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

The risk for the mother of later acquiringradiation-inducedbreast cancer seems to be particularly high for radiation doses during pregnancy.^[6]

This is an important factor when for example determining whether aventilation/perfusion scan (V/Q scan) or aCT pulmonary angiogram (CTPA) is the optimal investigation in pregnant women with suspectedpulmonary 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 theUnited Kingdom in 2005 considered CTPA to be generally preferable in suspected pulmonary embolism in pregnancy because of highersensitivity and specificity as well as a relatively modest cost.^[7]

• Radiobiology

• Human pregnancy
• Medical imaging

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