Use of a Cervicometer in Assessing Cervical Length and Risk of Preterm Birth

Abstract

INTRODUCTION: Although current obstetric practice guidelines suggest cervical length assessment in singletons for preterm birth risk, transvaginal ultrasonography has availability limitations. CerviLenz is a disposable device to measure vaginal cervical length. We sought to determine the threshold CerviLenz measurement with optimal specificity and sensitivity for diagnosis of short cervix by transvaginal ultrasonography and compare the abilities of CerviLenz and transvaginal ultrasonography to predict preterm birth. METHODS: Women with singleton pregnancies and no cervical anomalies or surgery or premature labor were consented, enrolled, and followed to delivery. Transvaginal ultrasonography and CerviLenz cervical length measurements were obtained by independent examiners at 17–23 weeks of gestation. A central reader certified sonographers and reviewed all transvaginal ultrasound scans. RESULTS: Based on 358 patients, receiver operator curves indicated optimal CerviLenz threshold of 30 mm to detect short cervix (transvaginal ultrasound cervical length at or below 25 mm). CerviLenz detected a short cervix with a negative predictive value (NPV) of 100%, sensitivity of 100%, and specificity of 46% (Table 1). Preterm birth before 37 weeks of gestation occurred in 25 (7%) patients. Area under the curve analyses for preterm birth before 28, 32, or 35 weeks of gestation revealed similar results for CerviLenz and transvaginal ultrasonography. For preterm birth before 37 weeks of gestation, CerviLenz had greater sensitivity (60%, transvaginal ultrasonography 16%) and transvaginal ultrasonography had higher specificity (97%, CerviLenz 44%).CONCLUSIONS: At a 30-mm threshold, CerviLenz has high NPV, high sensitivity, and moderate specificity to detect a short cervical length in the second trimester. CerviLenz is similar to transvaginal ultrasonography in prediction of preterm birth at 28–37 weeks of gestation. Based on high NPV, CerviLenz is clinically useful in identifying women not at risk for preterm birth, having potential to substantially reduce the need for transvaginal ultrasound screening in singletons.