Fetal MRI, the buzzword in antenatal care

Dr Ruchira Marwah

Antenatal care today is an integral part of the healthcare delivery system in pregnant women. A lot of emphasis is being given to antenatal health so that the disease processes affecting the child can be diagnosed early enough to reduce the morbidity and mortality associated with it. With the changing lifestyle scenario of the working class and one or two children in a family becoming the norm, each pregnancy becomes a precious pregnancy. A large number of diagnostic investigations are ordered to ensure fetal well-being. Imaging in the form of ultrasonography has long been used for monitoring fetal well-being during pregnancy and for the detection of any pregnancy related complications. Ultrasound examination has been popular because of the excellent information it provides for the doctor and patient, its easy availability and lack of harmful radiation to the fetus. In the last few years, MRI examination of the fetus has proved to be a useful adjunct to ultrasound examination.

Fetal MRI is primarily used to evaluate fetal abnormalities and provide more accurate information to help the parents make a well-informed decision about continuing or terminating pregnancy. Fetal MRI also helps to confirm the abnormalities detected on ultrasonography and to evaluate abnormalities not detected by ultrasound.

Since, MRI does not involve exposure to ionising radiation, it is especially useful for investigating pregnant women in whom other forms of diagnostic imaging are inadequate and would otherwise require exposure to ionising radiation like X-rays, CT scan etc.

MRI currently is being used for detecting and confirming craniospinal anomalies like ventriculomegaly, posterior fossa lesions, callosal anomalies, abnormalities of cerebral myelination, migration and sulcation, diastemotomyelia, segmental spinal dysgenesis and myelomeningocele spectrum. Abnormalities like diaphragmatic hernia, omphalocele and genitourinary abnormalities can also be diagnosed. MRI plays an important role in characterising head or neck masses, their relationship with other adjoining structures and the extent of airway compression.

This information could be crucial for planning the mode of delivery and airway management at birth. Information regarding such abnormalities can be useful for planning in-utero interventions, to guide the procedure and to prevent any complications after the procedure and for follow-up of these patients.

In cases, where ultrasound is able to provide only limited information due to sub-optimal fetal position, maternal obesity and severe oligohydramnio, fetal MRI can play a major role in antenatal assessment of such cases. In patients with large abdominal masses, the large field of view provided by MRI clarifies the diagnosis. Certain fetal anomalies and anatomic details are better characterised on MR than ultrasonography, which can affect fetal prognosis and selection for prenatal therapy.

Patients selected for fetal MRI scanning are fetal surgery candidates who are undergoing a multi-disciplinary evaluation for a congenital anomaly that is a potentially correctable lesion or a diagnostic dilemma.

Fetal MR examination requires no maternal preparation or fetal sedation. With newer ultrafast MRI techniques and better sequences, chances are minimal that fetal movement will affect the quality of the scan, thereby preventing the need for maternal fasting or fetal sedation.

One pertinent question that arises in the mind of any pregnant mother undergoing MRI for fetal assessment is “How safe it is for the child?”

Till date, no adverse effects have been demonstrated in literature and the MR procedure is not believed to be hazardous to the fetus. There are no known biological risks of MRI and no delayed sequelae have been encountered. In fact, MRI can be safely performed in the second and third trimester.

However, since the fetal cells are more susceptible to damage by various physical agents during organogenesis, it is better avoided during the first trimester, till a time more conclusive data is available regarding the safety of MRI in the first trimester of pregnancy. Also, contrast-enhanced MRI, which is the use of gadolinium, is not recommended in pregnancy since this contrast agent is known to cross placenta.

In India, as of today, fetal MRI examination is not very popular because of limited availability of expertise needed for adequate analysis and lack of awareness in the public and referring clinicians as to its potential uses.

It is high time, available advances in medical technology be utilised to their optimum potential to bring healthy babies into this world and helping prospective parents to take decisions about continuing or terminating pregnancy for reasons other than the sex of the unborn child.

The writer is radiologist, department of CT and MRI, Bombay hospital. Email: dr—atulmarwah@hotmail.com