Cervical length assessment using magnetic resonance imaging during pregnancy: correlation and agreement with transvaginal ultrasound.

Abstract

To assess the correlation between cervical length (CL) measurements obtained via fetal magnetic resonance imaging (MRI) and transvaginal ultrasound (TVS), and the accuracy of CL measurements obtained via MRI in diagnosing a second-trimester short cervix, using TVS as the gold standard. This was a retrospective cross-sectional study of pregnancies referred to our center between January 2022 and December 2024 that underwent fetal MRI and TVS examination on the same day. We estimated the correlation between MRI- and TVS-derived CL measurements using Spearman's rank correlation coefficient, with stratified analysis by pertinent clinical variables. Bland-Altman analysis was used to evaluate the agreement between the two imaging methods. Finally, for the subset of patients examined in the second trimester, we calculated the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of CL ≤ 25 mm on fetal MRI for predicting a short cervix with CL < 25 mm on TVS. We screened 132 patients, of whom 31 were excluded owing to incomplete data and one was excluded due to having a cervical cerclage in place. Therefore, 100 patients were included for analysis. There was a strong correlation between MRI- and TVS-derived CL measurements (r = 0.775; P < 0.001), which remained significant regardless of maternal body mass index, pregnancy type (singleton vs multiple) and CL on TVS (< 25 mm vs ≥ 25 mm). According to the Bland-Altman analysis, the mean difference in CL measurements between MRI and TVS was -0.97  (95% limits of agreement, -13.67 to 11.73) mm. The sensitivity, specificity, PPV and NPV of MRI-derived CL ≤ 25 mm for predicting a short cervix on TVS in the second trimester were 100% (95% CI, 59.0-100%), 94.6% (95% CI, 86.9-98.5%), 63.6% (95% CI, 30.8-89.1%) and 100% (95% CI, 94.9-100%), respectively. CL measurements obtained using fetal MRI correlate with those obtained using TVS. MRI-derived CL estimates may help to exclude a short cervix during pregnancy in selected patients undergoing MRI for other indications. However, larger studies are needed to validate our findings, and TVS remains the gold standard for cervical assessment during pregnancy. © 2026 International Society of Ultrasound in Obstetrics and Gynecology.