331 Correlation between MRI and transvaginal-ultrasound cervical length measurements in pregnancies complicated by twin-twin transfusion syndrome

Abstract

Twin pregnancies are at high risk of preterm birth, especially when complicated by twin-twin transfusion syndrome (TTS). Pregnancies with TTTS that are candidates for selective fetoscopic laser photocoagulation (SFLP) at our institution undergo transvaginal ultrasound (TVUS) and MRI evaluation of cervical length (CL) to assess preterm birth risk during the perioperative period. There is a paucity of data on accuracy of MRI for cervical length screening in high-risk pregnancies. We sought to investigate the correlation of CL between the two imaging modalities Retrospective cohort study comparing TVUS to MRI measures of CL in pregnancies that underwent SFLP for TTTS at a single center, 4/2010-6/2019. Among 626 pregnancies, data on pre-operative TVUS (n=579), MRI (n=424), and post-op TVUS (n=596) CL measures were available for analysis. Correlation was estimated using Pearson’s coefficient, mean CL measurements were compared with two-tailed paired T-test, and frequency of short cervix detection by the two imaging modalities was compared with chi-square The mean pre-op CL by MRI was an average of 3 mm shorter than the TVUS CL, 39 vs 42mm, respectively (p=0.002). The frequency of short CL ≤25 mm was 39(6.7%) by TVUS and 47(10.8%) by MRI, p=0.0001. CL measures by MRI correlate with TVUS overall (r=0.64); however, the correlation is poor at the shortest cervical lengths (r<0.20), see figure. MRI missed n=2(40%), 3(18.8%), 9(32.1%), and 13(28.9%) of CL cases detected as short by TV US at cut-offs of ≤15, 20, 25 and 28 mm, respectively. Sensitivity analyses excluding or adjusting for cerclage and pessary did not alter these findings Although MRI measurement of CL correlates well with TVUS overall, it performs poorly to accurately detect short cervix. Although prenatal MRI has some fetal anatomic diagnostic advantages over ultrasound, TVUS remains the optimal screening modality for cervical length in pregnancies at high-risk of preterm birthView Large Image Figure ViewerDownload Hi-res image Download (PPT)