Magnetic Resonance Imaging (MRI) is a medical imaging technique that uses strong magnetic fields and radio waves to generate detailed images of organs and soft tissues inside the body. Unlike X-rays or CT scans, MRI does not use ionizing radiation. This distinction is relevant for pregnant individuals, as safety concerns often arise. Understanding MRI’s function and implications for pregnant individuals is important for informed healthcare decisions.
General Safety of MRI During Pregnancy
MRI is considered safe for use throughout pregnancy, as it does not involve ionizing radiation, which is harmful to a developing fetus. The technology relies on magnetic fields and radio waves, and studies have not identified any adverse biological effects on fetuses from MRI exposure. Major medical organizations, including the American College of Radiology (ACR) and the American College of Obstetricians and Gynecologists (ACOG), state MRI can be performed in any trimester.
While no conclusive evidence of harm exists, some guidelines suggest caution during the first trimester. This is due to the theoretical risk of thermal effects from radiofrequency energy, as the developing fetus is sensitive during this period of organ formation. However, a large cohort study found no increased risk of harm to the fetus from first-trimester MRI exposure. The decision to perform an MRI during pregnancy is always a medical one, carefully weighing the potential benefits of obtaining diagnostic information against any theoretical risks to the mother and fetus.
When MRI is Used During Pregnancy
Ultrasound is the first-line imaging during pregnancy, but MRI is used when ultrasound results are inconclusive or insufficient for diagnosis. MRI offers more detailed soft tissue images, useful for assessing conditions in the pregnant individual or fetus.
For the pregnant individual, MRI might be indicated to evaluate acute abdominal pain, neurological conditions, or suspected placental abnormalities like placenta previa or placenta accreta. When assessing the fetus, MRI can provide further insights into suspected anomalies of the brain, spine, or other organs that were initially identified or not fully characterized by ultrasound. This detailed information guides prenatal counseling, delivery planning, and postnatal care.
Considerations for Contrast Agents
While MRI is considered safe during pregnancy, gadolinium-based contrast agents (GBCAs) are generally avoided unless absolutely necessary. Gadolinium crosses the placenta and enters fetal circulation, raising concerns about its retention in fetal tissues. Although human studies have not definitively shown adverse effects, animal studies have raised some concerns, and long-term safety data in humans is limited.
Professional guidelines, including the American College of Radiology, recommend avoiding routine GBCA administration during pregnancy. If a GBCA is considered, it is only after a thorough discussion between the radiologist, the referring physician, and the patient about the potential benefits outweighing the unknown risks to the fetus. In such cases, informed consent is obtained, acknowledging the cautious approach to these agents during pregnancy.
What to Expect During the Procedure
Undergoing an MRI while pregnant is similar to the procedure for non-pregnant individuals, with some additional considerations for comfort and safety. You will lie on a movable table that slides into a large, tube-like scanner. Remaining as still as possible is important during the scan, which lasts 30 to 60 minutes, depending on the area imaged.
The MRI machine produces loud thumping and buzzing noises, so earplugs or headphones will be provided. For comfort, especially later in pregnancy, you may be positioned with bolsters or allowed to lie partially on your side. Before the scan, you will need to remove all metal objects and jewelry, and a safety questionnaire will be completed to ensure no metallic implants are present that could interfere with the magnetic field. Communicate with the medical team throughout the process; they can address concerns like claustrophobia to ensure a comfortable, safe experience.