What question did this study set out to answer?

The study aims to assess the clinical value of MRI when used with expert ultrasound for diagnosing placenta accreta spectrum.

March 22, 2026Open Access

Use of magnetic resonance imaging as an adjunct to ultrasound for prenatal detection of placenta accreta spectrum

Key Points

The study aims to assess the clinical value of MRI when used with expert ultrasound for diagnosing placenta accreta spectrum.
Conducted as a multi-site retrospective cohort study across two tertiary maternity centers.
Included patients with clinical risk factors and ultrasound findings suspicious for PAS who underwent adjunctive MRI.
Classified PAS risk levels based on ultrasound and MRI reports, later confirmed by intraoperative findings.
Compared diagnostic performance between MRI and ultrasound, analyzing agreement and clinical outcomes.
Out of 70 patients, 56 (80%) were diagnosed with PAS.
MRI sensitivity was 0.83 and specificity was 0.24, compared to ultrasound sensitivity of 0.88 and specificity of 0.62.
Overall agreement between ultrasound and MRI was low at 44%, with only 27% of cases showing correct concordance.
In 34.5% of cases, MRI misclassified the disease severity, leading to disagreement with ultrasound findings.
Disagreement was not linked to differences in clinical outcomes or interventions.

Abstract

Background: Magnetic resonance imaging (MRI) is often routinely used to complement ultrasound for the prenatal diagnosis and surgical management of placenta accreta spectrum (PAS).However, several studies suggest there is no additional benefit of MRI, and it requires additional costs and resources.Furthermore, centers are gaining more expertise in ultrasound, frequently using it to correlate to the expected surgical topography, further questioning the role of MRI which typically was reported to provide additional information for surgical planning.Objectives: To evaluate the additional clinical value that MRI adds when used routinely as an adjunct to expert ultrasound for the prenatal detection and severity assessment of PAS within a specialist multidisciplinary service. Study design:A multi-site retrospective cohort study conducted across two tertiary maternity centres (2018)(2019)(2020)(2021)(2022)(2023).Consecutive patients with clinical risk factors and ultrasound findings suspicious for PAS who underwent adjunctive antenatal MRI and gave birth at a participating centre were included.Ultrasound and MRI reports classified PAS risk as low, suspected mild disease, or suspected severe disease.Final diagnosis and grading were determined by intraoperative findings and histopathology.Diagnostic performance of MRI and ultrasound was compared, along with agreement between modalities and associations with clinical management and outcomes.Results: 70 patients were included, of whom 56 (80%) were diagnosed with PAS.MRI demonstrated a sensitivity of 0.83 (95% CI 0.70-0.92)and specificity of 0.24 (95% CI 0.07-0.50),compared with ultrasound sensitivity of 0.88 (95% CI 0.76-0.95) and specificity of 0.62 (95% CI 0.32-0.86).Overall agreement between prenatal ultrasound and MRI was low at 44%, with correct concordance in only 27% of cases.In 34.5% of cases, MRI incorrectly disagreed with the ultrasound impression, most commonly by misclassifying disease severity.Disagreement between modalities was not associated with differences in gestational age at delivery, rate of Caesarean hysterectomy, estimated blood loss, or use of interventional radiology procedures. Conclusion:The role of MRI as a routine complementary imaging modality to US in a specialist, moderate volume PAS service is uncertain and may incorrectly change the suspected diagnosis.Where expert ultrasound is available, given the additional cost and resources required, the use of routine MRI in this setting warrants further exploration and may be better reserved for select cases.

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