To assess the diagnostic performance of transabdominal sonographic measurement of cervical length in identifying patients with a short cervix.
Cervical length was measured in 220 pregnant women using transabdominal and transvaginal ultrasound (US). Reproducibility and agreement between and within both methods were assessed. The diagnostic accuracy of transabdominal US for identifying cases with a cervical length <25mm was evaluated.
Twenty-one out of 220 cases (9.5%) had a cervical length <25mm by transvaginal US. Only 43% (n=9) of patients with a short cervix were correctly identified by transabdominal US. In patients with a cervical length of <25mm by transvaginal US, transabdominal measurement of the cervix overestimated this parameter by an average of 8mm (95% LOAs: −26.4 to 10.5mm). Among women without a short cervix, transabdominal US underestimated cervical length on average (LOA) by 1.1mm (95% LOAs: −11.0 to 13.2mm). Transvaginal US was also more reproducible (intraclass correlation coefficient: (ICC: 0.96; 95% CI: 0.94 to 0.97) based on comparisons between 2D images and immediately acquired 3D volume datasets relative to transabdominal US (ICC: 0.71; 95% CI: 0.57 to 0.84). Transvaginal US detected 13 cases with funneling and 6 cases with sludge whereas only 3 cases of funneling and one of sludge were detected by transabdominal US.
Transabdominal measurement overestimated cervical LOA by 8mm among women with a short cervix and resulted in the underdiagnosis of 57% of cases.
Keywords: ultrasound, agreement, preterm labor, screening, progesterone, progestins