The Use of MRI in Pregnancy: Benefits and Applications

Magnetic resonance imaging during pregnancy has emerged as a valuable diagnostic tool, particularly when ultrasound findings are unclear or incomplete. While ultrasound remains the primary imaging method for prenatal evaluation, MRI is not associated with risk and serves as an important complementary technique for assessing complex fetal and placental conditions. Understanding when and how to use MRI during pregnancy can significantly impact maternal and fetal care decisions.

Why MRI matters in pregnancy care
Safety considerations during pregnancy
Diagnosing fetal brain abnormalities
Assessing placental health and position
When MRI provides answers ultrasound cannot
Understanding gadolinium contrast considerations
Making informed decisions about fetal MRI

Why MRI matters in pregnancy care

MRI offers distinct advantages over ultrasound in certain clinical situations. The technique provides high-resolution images of the fetal brain and detailed views of structures such as the lungs, liver, kidneys and bowel, with superior soft tissue contrast and a large field of view making it particularly valuable for assessing complex anomalies. Unlike ultrasound, MRI performance is not significantly hindered by maternal obesity, fetal positioning, or reduced amniotic fluid, allowing for more comprehensive evaluation in challenging cases.

When ultrasound detects or suspects fetal brain abnormalities, MRI provides additional diagnostic information in nearly half of cases and leads to changes in clinical management in more than one-third of situations. This enhanced diagnostic accuracy helps healthcare providers offer more precise counseling to expectant parents about their baby’s condition and plan appropriate postnatal care.

Safety considerations during pregnancy

One of the most important questions about fetal MRI concerns its safety. The American College of Radiology and Society for Pediatric Radiology practice parameters, revised in 2024, cite data showing no conclusive harmful effects of 1.5 Tesla or 3 Tesla MRI on the developing fetus. Studies examining thousands of pregnancies have found no significant differences in birth weight, hearing function, or developmental outcomes between fetuses exposed to MRI and those not exposed.

However, the Canadian Association of Radiologists recommends that 1.5 Tesla MRI is preferred in the first trimester if both field strengths are available, reflecting a cautious approach during the most critical period of fetal development. The theoretical concerns about MRI during pregnancy include potential tissue heating from radiofrequency energy and acoustic noise exposure, but research has consistently shown these effects remain within safe limits when proper protocols are followed.

Diagnosing fetal brain abnormalities

MRI excels at detecting and characterizing fetal brain anomalies that may be difficult to assess with ultrasound alone. The technique allows safe and accurate anatomical assessments of fetal brain structures that serve as a foundation for prenatal diagnosis and counseling. Common indications include ventriculomegaly, corpus callosum abnormalities, and posterior fossa malformations.

The enhanced soft tissue contrast of MRI provides superior visualization of developing brain structures. MRI can detect anomalies not visible on ultrasound, allowing better visualization and characterization of brain structures with relevant implications for parent counseling and pregnancy management. This is particularly important for conditions like cortical malformations, which may only become apparent later in pregnancy and can significantly impact neurodevelopmental prognosis.

Timing matters when performing fetal brain MRI. The examination is typically indicated from 18 to 20 weeks of gestational age onwards, after expert neurosonography has been performed. Before 18 weeks, the small size of the fetus and motion artifacts limit the diagnostic value of MRI. The procedure is most commonly requested when ultrasound reveals abnormal findings or when pregnancy is at risk for brain injuries due to conditions like twin-twin transfusion syndrome or maternal infections.

Assessing placental health and position

Beyond fetal imaging, MRI plays an important role in evaluating placental conditions. MRI provides valuable information about the fetus, uterus, placenta and detailed assessment of maternal pelvic anatomy. This comprehensive view is particularly helpful when ultrasound assessment of the placenta is inconclusive or incomplete.

One critical application involves diagnosing abnormal placental attachment. When sonographic assessment of the placenta is inconclusive, MRI serves as an important adjunctive imaging test for diagnosing placenta accreta, increta, or percreta. These conditions, where the placenta attaches too deeply into the uterine wall, can lead to severe complications during delivery. Early diagnosis allows for proper planning and significantly reduces maternal morbidity.

Advanced MRI techniques can detect alterations in placental structure and function using insights into physiological adaptations and pathological processes. These methods help identify placental dysfunction in conditions like fetal growth restriction and congenital heart disease, providing information that can guide clinical management and improve outcomes.

When MRI provides answers ultrasound cannot

Several clinical scenarios particularly benefit from MRI evaluation. When ultrasound shows complex or multiple fetal anomalies, MRI’s multiplanar imaging and wide field of view enable comprehensive assessment of the entire fetal anatomy. MRI has advantages in demonstrating pathology of the brain, lungs, complex syndromes, and conditions associated with reduction of amniotic fluid.

The technique also proves valuable when maternal body habitus limits ultrasound visualization or when detailed characterization of a known abnormality is needed for surgical planning. In some cases, MRI helps differentiate between similar-appearing conditions that have vastly different prognoses, enabling more accurate counseling of expectant parents about what to expect after birth.

Understanding gadolinium contrast considerations

While non-contrast MRI is considered safe during pregnancy, the use of gadolinium-based contrast agents requires careful consideration. Gadolinium use should be limited to situations where benefits clearly outweigh possible risks. These contrast agents cross the placenta and are excreted by the fetal kidneys into the amniotic fluid, raising theoretical concerns about prolonged fetal exposure.

Research on gadolinium safety has yielded mixed findings. One large study raised concerns about possible associations with certain outcomes, but more recent research found that risk for pregnancies exposed to gadolinium-based contrast agents was similar to those exposed to MRI without contrast, with no significant increase in neonatal intensive care admissions. The current recommendation is to use gadolinium only when absolutely essential for obtaining critical diagnostic information that cannot be gained through other means.

Making informed decisions about fetal MRI

The decision to perform MRI during pregnancy should balance the diagnostic benefits against theoretical risks. The most important factor in having a healthy baby is ensuring a healthy mother, and necessary diagnostic imaging should not be refused due to unfounded fears. When a serious maternal or fetal condition requires clarification, MRI can provide crucial information that guides appropriate treatment and management.

Healthcare providers typically recommend fetal MRI when ultrasound findings are abnormal or inconclusive, when there is high suspicion of fetal anomalies despite normal ultrasound, or when detailed information is needed for pregnancy management decisions. The examination is performed by specialized technologists and interpreted by radiologists with expertise in fetal imaging, ensuring optimal image quality and accurate diagnoses.

What do you think? How might improved access to fetal MRI technology change prenatal care and outcomes in your community? What questions would you want answered before agreeing to fetal MRI if your healthcare provider recommended it?

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Table of Contents

Why MRI matters in pregnancy care 🔗

Safety considerations during pregnancy 🔗

Diagnosing fetal brain abnormalities 🔗

Assessing placental health and position 🔗

When MRI provides answers ultrasound cannot 🔗

Understanding gadolinium contrast considerations 🔗

Making informed decisions about fetal MRI 🔗