Foetal MRI

Author: Dr Michelle Fink*

What are the prerequisites for having a foetal MRI done?

Foetal MRI may complement ultrasound examination when detailed evaluation is required of intracranial and intrathoracic structures. It is also valuable when planning ante- or early postnatal surgical foetal intervention (e.g. in spina bifida, congenital diaphragmatic hernias, neck masses obstructing the airway). Unlike ultrasound, foetal MRI is not impaired by bone or gas in the foetal skeleton or maternal abdomen. It provides better contrast resolution and a larger field of view than conventional ultrasound.

Foetal MRI images are visually easier than corresponding ultrasound images for people who are not foetal imaging specialists to understand. For this reason, they can be helpful for families seeking to understand the anatomy of a complex foetal problem.

Foetal MRI tests are used to help clarify unanswered questions after evaluation of a pregnancy at a multidisciplinary foetal medicine unit.

It should therefore only be requested after comprehensive tertiary level clinical and ultrasound assessment of the mother and foetus.

What are the absolute contraindications for a foetal MRI?

Foetal MRI must not be carried out in the first trimester of pregnancy, because diagnosis accuracy is less at that time.

As in all MRI examinations, should the mother have any implants (e.g. stents, pacemaker), these must be proven to be MRI compatible before the examination. The usual precautions with respect to metallic foreign bodies (such as body piercings) apply.

Contrast agents are not administered during foetal MRI, as they cross the placenta and are recycled in the foetus by urinary excretion and swallowing of the amniotic fluid. When MRI is carried out for urgent maternal indications, contrast agents may still be given as the benefit outweighs the risk.

What are the relative contraindications for a foetal MRI?

• Maternal claustrophobia.
• Extreme overweight (which would compromise placing the patient in the MRI scanner).

What are the adverse effects of a foetal MRI?

Foetal MRI has no known adverse effect on either the mother or the foetus.

Are there alternative imaging tests, interventions or surgical procedures to a foetal MRI?

Ultrasound examination remains the primary modality for imaging the foetus in utero. The advantages of ultrasound over MRI are its wide availability, superior spatial resolution and it being unaffected by foetal movement. Being a real-time examination, it also provides functional data, including Doppler evaluation.

Useful websites about foetal MRI:

• RCH Melbourne policies and procedures – Foetal MRI:
  www.rch.org.au/policy_rch/?doc_id=9605
• RCH Melbourne – Kids health info for parents – Foetal MRI:
  www.rch.org.au/kidsinfo/factsheets.cfm?doc_id=5790
• Postgraduate Medical Journal: Review of MRI in foetal medicine 2010:
  pmj.bmj.com/content/86/1011/42.full

*The author has no conflict of interest with this topic.

Page last modified on 26/7/2017.