Fetal MRI

Fetal MRI is a problem-solving adjunct to obstetric ultrasound, most often used to clarify central nervous system anomalies and to characterise thoracic, abdominal and placental abnormalities. Ultrafast T2 sequences freeze fetal motion without sedation, and the examination is performed without gadolinium to avoid fetal exposure, usually after the first trimester.

Indications

Confirmation and characterisation of CNS anomalies (ventriculomegaly, agenesis of the corpus callosum, posterior fossa malformations, cortical malformations)
Thoracic lesions: congenital pulmonary airway malformation, congenital diaphragmatic hernia and lung volume assessment
Abdominal and pelvic masses, bowel and genitourinary anomalies
Complex or equivocal ultrasound findings limited by maternal habitus, oligohydramnios or fetal position
Assessment of placenta accreta spectrum and complicated monochorionic twin pregnancies
Surgical/fetal intervention planning and prognostication

Contraindications & Cautions

Non-conditional maternal implants (pacemakers, ICDs, neurostimulators) and ferromagnetic devices
First trimester is generally avoided; imaging is preferred after 18 weeks when justified
Maternal severe claustrophobia or inability to lie still/supine (use left lateral decubitus)
Gadolinium is contraindicated (crosses the placenta and recirculates in amniotic fluid)
Sedation is avoided; rely on ultrafast motion-tolerant sequences

Patient Preparation

Maternal MRI safety screening and confirmation of gestational age
No fasting required; empty bladder for comfort
Position supine or left lateral decubitus to avoid aortocaval compression in later pregnancy
Explain repeated short breath-holds and reassure regarding safety without contrast or radiation
Plan sequences relative to the fetal (not maternal) anatomical planes and re-localise as the fetus moves

Technique & Parameters

Ultrafast single-shot T2 (SSFSE/HASTE) in three orthogonal fetal planes as the primary sequence
Balanced steady-state free precession (true FISP/FIESTA) for vessels, heart and fluid interfaces
Echo-planar T2* to detect haemorrhage, calcification and bone
T1-weighted gradient-echo to demonstrate meconium, fat, haemorrhage and thyroid/liver signal
Diffusion-weighted imaging for the brain and kidneys where indicated
1.5T is preferred over 3T for a favourable specific absorption rate and fewer artefacts; small field-of-view and multiple short acquisitions

Systematic Review

Confirm number of fetuses, lie, placental position and amniotic fluid
Assess fetal brain: biometry, ventricular width (atrium >10 mm abnormal), midline structures, posterior fossa and cortical sulcation for gestational age
Evaluate the face, neck and airway
Assess the thorax: lung volumes and signal, cardiac position, diaphragm integrity
Review the abdomen and pelvis: bowel signal (meconium T1-bright), kidneys, bladder and abdominal wall
Examine the spine, limbs and the placenta/myometrial interface

Key Findings & Significance

Ventriculomegaly with atrial width >10 mm and associated anomalies affecting prognosis
Agenesis of the corpus callosum with colpocephaly, parallel ventricles and absent cavum septi pellucidi
Posterior fossa anomalies: Dandy-Walker malformation, vermian hypoplasia, Blake pouch cyst
Congenital diaphragmatic hernia with herniated viscera and reduced lung volume; measured lung-to-head ratio for prognosis
Congenital pulmonary airway malformation or sequestration as a T2-hyperintense lung lesion
Placenta accreta spectrum: dark intraplacental T2 bands, myometrial thinning and bladder-wall interruption

Differential Considerations

Cystic posterior fossa: Dandy-Walker malformation, mega cisterna magna, Blake pouch cyst, arachnoid cyst
Fetal chest mass: CPAM, sequestration, congenital diaphragmatic hernia, bronchogenic cyst
Abnormal bowel signal: meconium peritonitis, atresia, cystic fibrosis-related changes
Intracranial cyst/midline abnormality: interhemispheric cyst, holoprosencephaly, arachnoid cyst
Abdominal cystic lesion: ovarian cyst, mesenteric cyst, duplication cyst, hydronephrosis

Pearls & Pitfalls

Fetal MRI complements, and does not replace, a detailed anatomy ultrasound; interpret them together
Gadolinium is avoided because it crosses the placenta and accumulates in amniotic fluid with unknown fetal effect
1.5T is generally preferred to keep the specific absorption rate low and reduce dielectric artefact
Meconium is characteristically T1-bright and T2-dark, helping to localise normal distal bowel
Sulcation and myelination milestones must be judged against gestational age to avoid overcalling delay

Structured Report

State gestational age, field strength, sequences and that no contrast or sedation was used
Report the targeted anomaly with measurements (e.g. ventricular atrial width, lung volumes/ratios)
Describe associated findings that alter prognosis and correlate with ultrasound
Comment on the placenta and amniotic fluid where relevant
Provide an impression with prognostic implications and multidisciplinary/counselling recommendation

References

Prayer D, et al. ISUOG Practice Guidelines: performance of fetal MRI. Ultrasound Obstet Gynecol
Griffiths PD, et al. MERIDIAN study: use of MRI in fetal brain abnormalities. Lancet
ACR-SPR Practice Parameter for the Safe and Optimal Performance of Fetal MRI
Saleem SN. Fetal MRI: an approach to practice. Radiographics

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.

Fetal MRI

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References