Fetal and Placenta MRLloyd Stambaugh, MD

Radia

Fetal MR Indications

• Fetal MR is most commonly used to assess the brain after an abnormal fetal sonogram• Absent CSP

• Ventriculomegaly

• Abnormal posterior fossa

• Most common Fetal MR abnormal findings• Absent corpus callosum

• Ventriculomegaly

• Dandy Walker variant

Less common indications

• Chest mass

• Abdomen/pelvic mass

• Spinal abnormality

MRI Safety and Pregnancy

• FDA requires MRI devices indicate the safety of MRI with respect to the fetus “has not been established.”

• 2007 ACR states all pregnant patients can receive MRI as long as the “risk-benefit ratio to the patient warrants that the study be performed.”

MRI Safety and Pregnancy

• Canadian study, all births > 20 gestation between 2003-2015

• 1.4M deliveries

• MRI rate 3.97 per 1000 pregnancies

• 1st trimester MRI stillbirth RR 1.68 (CI 0.97 to 2.9); adjust risk difference 4.7 per 1000 person-years

• No significant higher risk of congenital anomalies, neoplasm, vision or hearing loss.

• Conclusion – 1st trimester MRI exposure was not associated with increased risk of harm to the fetus or in early childhood.

JAMA. 2016 Sep 6;316(9):952-61

25 y.o. pregnant patient. Absent CSP and ventriculomegaly on ultrasound.

31 y.o. pregnant patient. Mild asymmetric ventriculomegaly.

Fetal Brain MR added value

• Meta-analysis of 27 articles, 1184 patients – compared US and MR of fetal brain

• US and MR agreed 65%

• MR showed additional/different pathology in 23%

• Compared with post-natal dx • MR agreed 80%

• US agreed 54%

• Fetal brain MR in addition to US improves diagnostic accuracy

J Matern Fetal Neonatal Med, 2016; 29(18): 2949-2961

Fetal MR additional value

• Systemic review of literature

• 13 articles, 710 fetuses

• MR confirmed US-positive findings in 65%

• Provided additional information in 22%

• MR additional findings changed management in 30%

• US/MR primarily agreed for ventriculomegaly, but more often disagreed for midline anomalies.

Ultrasound Obstet Gynecol 2014; 44: 388-393

Fetal MR additional value

• MERIDIAN Study -- Multicenter, prospective, cohort study with brain abnormality on US (16 fetal medicine centers, 570 patients)

• Diagnostic accuracy improved• 23% in 18-24 wk EGA group

• 29% in >24 week EGA group

• Overall accuracy• US 68%

• MR 93%

• MR provided additional information in 49% and changed prognosis in 20%

• MR influence on counseling• None 22%

• Minor 63%

• Major 15%

• MR contribution to management• None 12%

• Minor 53%

• Significant 26%

• Major 6%

• Decisive 3%35%

28 y.o. pregnant patient with abnormal ventricle on US

32 y.o. pregnant patient with abnormal posterior fossa on US, concerning for Dandy Walker

MR Placenta

Placenta Accreta Spectrum

• Risk factors• Previous cesarean section, particularly multiple

• Placent previa

• AMA

• Additional – multiparity/IVF/uterine surgery/fibroids/smoking/etc

• Placenta previa + 3 prior C-sections = 40% PAS

• No previa + 3 prior C-sections = <1% PAS

31 y.o. female at 28w2d with prior C-section, previa, and pain under C-section scar

34 y.o. pregnant female with prior C-section. Peripheral location of gestation sac in LUS

42 yo pregnant patient with abdominal pain & vomiting

Placenta percreta through right lower uterine segment. Large RLQ hematoma and hemoperitoneum.

36 y.o. pregnant female with prior C-section and probable placenta accreta/percreta by US

Placenta Accreta Spectrum – US vs MR

• US• Sensitivity 77% to 87%• Specificity 96% to 98%

• MR• Sensitivity 80% to 85%• Specificity 65% to 100%

• MR and US have similar sensitivity, but US is generally more specific

• MR is helpful• Posterior or lateral placenta• Extra-uterine organ involvement with percreta

Clinical Ob Gyn; vol 61, No4, 755-765

• Assessed 28 cases of suspected placenta accreta spectrum in third trimester; all cases received US & MR; surgical confirmation of diagnosis

• US• Sensitivity 0.96

• Specificity 0.6

• MR• Sensitivity 0.83

• Specificity 0.4

• Post-hoc MR structured scoring system improved sens 0.96/spec 0.6

J Matern Fetal Neonatal Med. 2020 Nov 12:1-4

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