Is Fetal MRI as Accurate as Ultrasound for Short Cervix?

Accurately predicting preterm birth remains a top priority in maternal-fetal medicine. Consequently, obstetricians rely heavily on accurate cervical length assessment during the second trimester of pregnancy. For decades, clinicians have considered transvaginal ultrasound (TVS) as the gold standard for this measurement. However, a new study by Schenone et al. demonstrates how fetal magnetic resonance imaging (MRI) serves as a reliable alternative.

The Importance of Cervical Length Assessment on MRI

The retrospective cross-sectional study evaluated 100 pregnant patients who underwent both fetal MRI and TVS on the same day. Specifically, the researchers excluded patients with incomplete data or those with a cervical cerclage in place. Their results revealed a remarkably strong correlation between MRI-derived and TVS-derived measurements (r = 0.775, p < 0.001). Furthermore, this significant correlation persisted regardless of maternal body mass index or pregnancy type. Therefore, fetal MRI offers a stable and independent diagnostic capability for assessing the cervix.

Diagnosing a Second-Trimester Short Cervix with MRI

In the second trimester, identifying a short cervix (less than 25 mm) is crucial to prevent pregnancy loss. Consequently, the researchers evaluated the diagnostic accuracy of MRI-derived measurements. Specifically, they analyzed the sensitivity and specificity of a cervical length of 25 mm or less on MRI. Amazingly, the MRI-derived measurements achieved 100% sensitivity and 94.6% specificity. Moreover, the negative predictive value reached a perfect 100%. Thus, clinicians can confidently rule out a short cervix using fetal MRI.

Clinical Implications for Practice

Transvaginal ultrasound remains the undisputed gold standard for cervical screening. However, fetal MRI serves as an invaluable adjunct or alternative in specific clinical scenarios. For instance, some patients might find transvaginal ultrasound highly uncomfortable or contraindicated. In addition, fetal MRI is frequently performed for other fetal anomalies, allowing a concurrent cervical evaluation. Therefore, radiodiagnosis teams should systematically measure and report the cervix during all prenatal MRI examinations. This holistic approach can significantly optimize maternal-fetal care.

Frequently Asked Questions

Q1: Why is cervical length assessment important during the second trimester?

An accurate cervical length assessment helps clinicians identify patients at risk of preterm birth. Consequently, a short cervix (less than 25 mm) prompts immediate medical interventions to prolong the pregnancy.

Q2: Can fetal MRI replace transvaginal ultrasound for measuring cervical length?

Transvaginal ultrasound remains the primary gold standard for routine screening. However, fetal MRI provides a highly accurate alternative with a 100% negative predictive value. Therefore, it is extremely useful when ultrasound is contraindicated or during concurrent fetal MRI exams.

References

1. Schenone CV et al. Cervical length assessment using magnetic resonance imaging during pregnancy: correlation and agreement with transvaginal ultrasound. Ultrasound Obstet Gynecol. 2026 Jul 10. doi: 10.1002/uog.70269. PMID: 42430210.
2. Dyer E. CPD Shorts: Cervical length assessment in pregnancy. SoR – Society of Radiographers. 2026 Mar 6.
3. Singh D, Bhagwat KA, Jeevika MU, Tyagi H. Role of cervical length measured on transvaginal ultrasound at 19-24 weeks in prediction of preterm labor. Int J Radiol Diagn Imaging. 2023;6(2):21-26.