Magnetic resonance imaging (MRI), without MRI contrast agents, is not associated with any risk for the mother or the fetus, and together with medical ultrasonography it is the technique of choice for 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. 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.
Gadolinium contrast agents in the first trimester is 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. In the second and third trimester, gadolinium contrast is associated with a slightly increased risk of stillbirth or neonatal death, by the same study. 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 outcome.
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. Appropriate use criteria by the American College of Radiology give a rating of ≥7 (usually appropriate) for non-contrast MRI for the following conditions:
Health effects of radiation may be grouped in two general categories:
|Gestational age||Embryonic age||Effects||Estimated threshold dose (mGy)|
|2 to 4 weeks||0 to 2 weeks||Miscarriage or none (all or nothing)||50 - 100|
|4 to 10 weeks||2 to 8 weeks||Structural birth defects||200|
|Growth restriction||200 - 250|
|10 to 17 weeks||8 to 15 weeks||Severe intellectual disability||60 - 310|
|18 to 27 weeks||16 to 25 weeks||Severe intellectual disability (lower risk)||250 - 280|
|Imaging method||Fetal absorbed dose of ionizing radiation (mGy)|
|Cervical spine by 2 views (anteroposterior and lateral)||< 0.001|
|Mammography by 2 views||0.001 - 0.01|
|Chest||0.0005 - 0.01|
|Abdominal||0.1 - 3.0|
|Lumbar spine||1.0 - 10|
|Intravenous pyelogram||5 - 10|
|Double contrast barium enema||1.0 - 20|
|Head or neck||1.0 - 10|
|Chest, including CT pulmonary angiogram||0.01 - 0.66|
|Limited CT pelvimetry by single axial slice through femoral heads||< 1|
|Abdominal||1.3 - 35|
|Pelvic||10 - 50|
|Low-dose perfusion scintigraphy||0.1 - 0.5|
|Bone scintigraphy with 99mTc||4 - 5|
|Pulmonary digital subtraction angiography||0.5|
|Whole-body PET/CT with 18F'||10 - 15|
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.