ABSTRACT
OBJECTIVES: To compare three methods of cervical length measurements using ultrasound in the first trimester: single-line, two-line, and tracing. METHODS: Images appropriate for cervical length measurements were obtained using transvaginal ultrasound between 11 + 0 and 13 + 6 weeks' gestation. The cervix was measured on stored images using three methods: a single straight line, two segments (two-line method), and by tracing the distance along the cervical canal. Results were compared for intraoperator repeatability and interoperator variability. The degree of the cervical curvature was measured. RESULTS: The mean cervical measurement using the single-line measurement was 32.8 (SD 4.4) mm. The mean cervical length was essentially the same using the two-line and tracing measurement: 34.4 (SD 4.7) mm and 34.5 (SD 4.7) mm, respectively. Both intra- and interoperator agreement was high. The degree of curvature of the cervical canal was variable, with a resultant variability in the difference between the single straight line measurement and the other two types of measurement. CONCLUSIONS: Using stored images, each of the measurement techniques is highly reproducible. Both the two-line and the tracing methods yield larger measurements than the single-line technique. Therefore, it appears that in select cases the straight line measurement significantly underestimates the actual cervical length.
