Fetal MRI - Indications, Procedure, and Contraindications

Introduction:

Normally, during pregnancy, ultrasound imaging is commonly used to measure the size of a fetus, evaluate the quantity of fluid around a fetus, check the cervix length, fetal activities, and check for congenital abnormalities. But in certain cases, ultrasound imaging will not be helpful. So to detect potential abnormalities, fetal MRI (magnetic resonance imaging) is used. MRI is operated with strong magnetic fields and radio waves to obtain images. Fetal MRI produces detailed images of the fetus from different angles without causing harm to the baby. Any abnormalities can be detected with fetal MRI and ultrasound imaging, and prenatal counseling or managing affected pregnancies can be done.

What Is Fetal MRI?

A fetal MRI is a non-invasive imaging test that provides detailed information about the anatomic structures of the fetus through clear and high-resolution images. Healthcare professionals order MRI when the condition is not properly checked with other imaging methods, such as ultrasound, CT (computed tomography) scan, and X-ray. MRI is also safer than other imaging tests like X-ray and CT scans. Fetal MRI provides information about the fetal brain, central nervous system, abdomen, and chest that cannot be collected from an ultrasound alone. The information collected from fetal MRI imaging allows the health care professional to understand better how various abnormalities interrupt the child’s development during pregnancy and after birth.

When Is Fetal MRI Indicated?

A fetal MRI is usually indicated when any abnormality is detected on ultrasound, difficulties in visualizing the fetal structures due to technical difficulties, or any conditions that can affect pregnancy, like fetal congenital heart diseases and family history of neurodevelopmental disorders. In the following situations, fetal MRI is often recommended:

• Brain and spine anomalies detected on ultrasound like posterior fossa abnormalities, any solid or cystic masses, cephalocele (a birth abnormality in which a portion of the brain and its protective covering protrude through a defect in the skull), cerebral cortical malformations, migrational anomalies, vascular malformations, ventriculomegaly, hemorrhage, infarct, or monochorionic twin pregnancy complications.

• Congenital anomalies of the spine, like vertebral anomalies, neural tube defects, sacrococcygeal teratomas (a type of tumor that develops at the base of the spine in infants and children), caudal regression (a rare disorder that affects the development of the lower half of the body), and sacral agenesis.

• Abnormalities in the head and neck, like congenital cysts or masses, suspected mass on the face or neck, clefts, teratoma, and lymphatic malformations.

• Abnormalities in the thorax, like congenital lung and airway malformations, congenital diaphragmatic hernias, esophageal atresia, mediastinal masses, effusions, and lung assessment in fetuses at risk for pulmonary hypoplasia.

• Abdominopelvic abnormalities include suspected masses or cysts, genitourinary anomaly, suspected anorectal malformation, complex bowel obstruction, difficulty in assessing by ultrasound, and abdominal wall defect.

• Musculoskeletal abnormalities like an assessment of suspected masses, dysplasias, or malformations.

• Multiple gestation pregnancies like monochorionic twins, conjoined twins, etc.

• Placental abnormalities that are not assessed in ultrasound imaging.

When Is Fetal MRI Performed?

A fetal MRI is not recommended in the first trimester of pregnancy. It is recommended after 18 weeks of pregnancy by the American College of Radiology (ACR) because the static magnetic fields effect, radiofrequency pulses, and rapidly changing gradients cannot define the fetus before 18 weeks of pregnancy. Therefore fetal MRI is normally recommended after an anomaly scan which is done around 20 to 22 weeks of pregnancy. In certain conditions, the fetal MRI scan may be postponed till 26 to 28 weeks of pregnancy, depending upon certain clinical indications. Even in the third trimester, a fetal MRI is recommended if there are abnormal findings in ultrasound or as a follow-up scan.

What Preparations Should Be Taken for a Fetal MRI Scan?

To get a high-quality MRI image, it is necessary to reduce fetal motion during the MRI. Fetal movement is more observed after the mother has taken food. So, it is often advised to mothers not to eat or drink anything for 3 to 4 hours before the scheduled fetal MRI appointment in order to reduce fetal motion during the scan. However, if the mother has observed fetal movement while avoiding food for a long time, then the mother should adjust her eating schedule accordingly. Also, it has been observed that fetal movements are less during the afternoon, so it is better to schedule the scan during that period of the day. Other things to consider during the fetal MRI are:

• No medications or injections are given before or during the scan.

• Mothers need not remain in the full bladder for the scan. Emptying the bladder 10 to 15 minutes before the scan is recommended to make the procedure more comfortable.

• All the metal items and electronic devices, like coins, jewelry, wristwatches, mobile phones, etc., should be removed before entering the examination room.

• When the mother is in a relaxed and in a comfortable position, the movement of the fetus is less observed. So, the mother can make herself comfortable by listening to music, reading books, etc.

• Walking slowly for 10 to 15 minutes before the procedure is advisable.

• Fetal MRI can not be used for sex determination of the baby, as per the act PC-PNDT. So the mothers are expected to fill up the forms and sign them before the scan.

What Happens During the Fetal MRI Scan?

An MRI technician will guide the patient throughout the procedure during the fetal MRI scan. The procedure usually takes around 35 to 40 minutes and can also prolong if the patient is not positioned properly or feels uncomfortable during the procedure.

• Initially, the patient is asked to lie on the MRI table, and a plastic cushioning wrap will be draped over the belly of the patient. If the patient feels uncomfortable lying down, a bolster can be placed under the knees to take the pressure off the lower back. Also, lying on the sides is an effective method.

• A hand switch will be provided for the patient to squeeze when they feel uncomfortable during the fetal MRI scan. Also, an ear plug or headphones will be given to the patient to minimize the loud noise produced by the MRI machine.

• Also, during the procedure, the technician will give instructions to breathe regularly and gently. And, usually, towards the end of the procedure, the technician will give instructions to hold their breath.

• If some patients feel claustrophobic during the procedures, oxygen will be provided, or a companion will be allowed in the room during the procedure.

When Is Fetal MRI Contraindicated in Pregnant Women?

Fetal MRI is contraindicated in certain pregnant women, including

• Claustrophobic women (fear of closed spaces).

• If the size or weight of the pregnant woman exceeds the MRI caliber or MRI table recommendations.

• Before 18 weeks of gestation.

• In the presence of implanted ferromagnetic devices.

• Rapid fetal heart rate and fetal movement.

Conclusion:

Fetal MRI is a non-invasive imaging test used for acquiring high-quality fetal images where ultrasound cannot provide the needed information. This imaging technique is proven to be safe for the fetus and is not painful. It is indicated only after 18 weeks of pregnancy. No special preparations are required for this procedure. The results can be collected by the end of the day, which healthcare professionals will observe, and further pregnancy management or pregnancy counseling will be provided to the parents.