Cervical length at 22-24 weeks of gestation: comparison of transvaginal and transperineal-translabial ultrasonography.

OBJECTIVES To investigate the feasibility of measuring cervical length by transperineal or translabial sonography and compare the measurements obtained by this approach with those obtained transvaginally. METHODS In 500 women measurement of cervical length by translabial-transperineal sonography was attempted immediately before transvaginal scanning at 22-24 (median 23) weeks of gestation. In the first phase of the study, considered to be the learning period, 200 patients were examined and their results reviewed, before carrying out the second phase in which 300 patients were examined. A comparison was made of the patient acceptability of both techniques. RESULTS Cervical length was successfully measured transvaginally in all cases. In the first phase of the study cervical length was measured by translabial-transperineal sonography in 84% of the 200 patients but there was poor agreement with measurements obtained transvaginally and the 95% tolerance interval for paired observations was -11.0 mm to 16.1 mm. After audit of results it became apparent that the translabially-transperineally derived images were inadequate in more than half of the cases but in those with adequate paired measurements there was a very good agreement between the two and the 95% tolerance interval for paired observations was -5.8 mm to 5.2 mm. In the second phase of the study special attention was paid towards recording measurements of cervical length only in cases where both the internal and external os were adequately visualized. Successful measurements by translabial-transperineal sonography were obtained in 78% of cases and the 95% tolerance interval for paired observations was -5.8 mm to 6.1 mm. The degree of patient acceptability of the two methods was similar. CONCLUSIONS The findings of this study suggest that at 22-24 weeks of gestation the cervix can be visualized adequately by translabial-transperineal sonography in about 80% of patients and the measurements of cervical length obtained by this approach are very similar to those obtained by transvaginal sonography.