Magnetic Resonance Imaging (MRI) is generally considered a safe diagnostic tool during pregnancy. It provides detailed images of the body’s internal structures without relying on ionizing radiation. This makes it a preferred option when medical imaging is necessary, offering a non-invasive way to gather important medical information about both the mother and the developing fetus.
Understanding MRI Safety During Pregnancy
MRI uses powerful magnetic fields and radio waves to create images, unlike X-rays or CT scans that use radiation. The strong magnetic field aligns protons within the body’s water molecules. Brief pulses of radio waves then temporarily disrupt this alignment, and as the protons realign, they emit signals that the MRI scanner detects. This process does not involve ionizing radiation, a key distinction.
The absence of ionizing radiation is a primary reason MRI is considered safe for pregnant individuals and their developing fetuses. Research and medical consensus indicate no known harmful effects from the magnetic fields or radiofrequency waves used in standard MRI scans. Major medical bodies, including the American College of Radiology (ACR) and the American College of Obstetricians and Gynecologists (ACOG), state that MRI is not associated with adverse fetal effects when clinically indicated.
While concerns about acoustic noise from the MRI scanner have been raised, studies show exposure during the second and third trimesters is not associated with an increased risk of neonatal hearing impairment. The imaging technique is designed to change the position of atoms without altering their structure or composition. This safety profile allows for necessary diagnostic evaluations without posing a recognized risk to the pregnancy.
Role of Contrast Agents in Pregnancy MRI
MRI sometimes involves gadolinium-based contrast agents (GBCAs) injected intravenously to enhance image clarity. These agents can improve the visibility of certain tissues or abnormalities, aiding in diagnosis.
However, GBCAs are used with significant caution during pregnancy because they cross the placental barrier and enter fetal circulation. While some studies lack conclusive evidence of adverse effects, research has suggested a potential increased risk of stillbirth, neonatal death, or certain inflammatory skin conditions in offspring after GBCA exposure.
Due to these concerns and unknown long-term effects, medical guidelines recommend avoiding routine GBCA administration during pregnancy. GBCAs should only be administered if the potential for significant clinical benefit to the mother or fetus clearly outweighs the potential, though unconfirmed, risks. If a contrast-enhanced MRI is deemed necessary, the decision is made after thorough discussion between the provider and patient, considering the urgent medical need.
Medical Reasons for an MRI During Pregnancy
MRI may be considered during pregnancy when other diagnostic methods are insufficient or when the information gained is essential for guiding medical management. This imaging provides highly detailed soft tissue contrast for diagnosing certain conditions.
For the pregnant individual, MRI might evaluate acute abdominal pain, such as suspected appendicitis, especially when ultrasound findings are unclear. It has shown high accuracy in diagnosing or excluding appendicitis in pregnant patients. MRI can also assess neurological issues, severe back pain unresponsive to conservative treatment, or placental abnormalities.
For the fetus, MRI often investigates anomalies detected on ultrasound, particularly for detailed evaluation of the brain and spine. This can include assessing conditions like ventriculomegaly, malformations of cortical development, or neural tube defects. Fetal MRI provides a more comprehensive view of complex anomalies or when factors like fetal position or maternal body habitus limit ultrasound visualization.
Other Imaging Options
Other imaging modalities are utilized during pregnancy, each with its own benefits and limitations. Ultrasound, or sonography, is widely considered a safe and routine part of prenatal care. It uses high-frequency sound waves to create real-time images of the fetus and maternal structures without using radiation. Ultrasound is a primary tool for confirming pregnancy, dating, monitoring fetal growth, and detecting many anomalies.
Imaging techniques using ionizing radiation, such as X-rays and Computed Tomography (CT) scans, are generally avoided during pregnancy unless absolutely necessary. X-rays use small amounts of radiation to image bones, and while most X-rays do not expose the fetus to radiation, abdominal X-rays carry a slight risk. CT scans involve multiple X-ray images, delivering higher radiation doses than standard X-rays. While the radiation dose from diagnostic CT scans is often low and unlikely to cause harm, there is a theoretical increased risk of childhood cancer, particularly if the abdomen or pelvis is directly imaged. Therefore, MRI and ultrasound are preferred whenever possible due to their non-ionizing nature.