How Reliable Is the Determination of Cervical Dilation? Comparison of Vaginal Examination With Spatial Position-Tracking Ruler

Abstract

The traditional method for assessment of cervical dilation—vaginal examination—is subjective and has an accuracy of less than 60%. Although several devices for cervical dilation assessment have been developed, few have survived and cervical assessment is still performed by vaginal examination worldwide. This prospective study compared the accuracy of clinical measurement of cervical dilation for 2 methods, vaginal examination and use of a position-tracking system. The study subjects, enrolled at 3 centers (Poissy, France; Brooklyn, NY; and Haifa, Israel), were 188 singleton women in active labor with vertex presentation and no known contraindication to vaginal examination. For each routine vaginal examination, a sensor was attached to the midwife’s index fingertip and measurement was performed with a magnetic position tracking system, using personal computer-based controlling software, and ultrasound imaging technology. A total of 333 measurements were performed with the tracking system. Ninety cases with clinically full dilation were excluded from analysis. The data from the 3 centers were pooled; results were similar in each. There was an overall mean absolute difference of 10.2 ± 8.4 mm between the 2 methods. Analysis of subgroups stratified by dilation showed that the absolute difference was 7.5 ± 7.3 mm (70.0% accuracy) when the cervical dilation was >8 cm and 12.5 ± 8.7 mm (38.8% accuracy) when the cervical dilation was between 6.1 and 8 cm. These findings show that the accuracy of the positron-tracking system for assessment of cervical dilation during labor appears to be limited. The clinical relevance of this system in routine care is unclear and requires further evaluation.