Comparison of transvaginal sonography with digital examination and transabdominal sonography for the determination of fetal head position in the second stage of labor

Abstract

Objective: Precise determination of fetal head position in labor is a prerequisite for safe instrumental deliveries, and essential for the assessment of labor progress. Recent studies have cast serious doubts on the accuracy of the time-honored digital vaginal examination (DVE) in comparison to transabdominal ultrasound scans (TUS). However, transabdominal imaging is technically difficult with a deeply engaged fetal head in the second stage of labor. We examined the accuracy and time requirements of transvaginal scans (TVS) in the second stage of labor for determination of fetal head position.

Study design: Sixty laboring women in the second stage of labor with a deeply engaged fetal head were examined by experienced nurse midwives and senior residents. Fetal head position was recorded as "time on a 12-hour clock." Subsequently, TUS and TVS were independently performed by a skilled sonographer. Accuracy and time requirements for all 3 examinations were recorded.

Results: Fetal head position could be determined in all cases by TVS, but not in 7 cases and 9 cases by DVE and TUS, respectively (P < .03; P < .008). A discrepancy of 60 degrees or more between the DVE and TUS or TVS was found in 13/60 cases (21.7%) and 14/60 cases (23.3%), respectively. A > or = 90 degrees discrepancy was found in 9/60 cases (15%) and 12/60 cases (20%), respectively (P < .02 for comparison of TUS and TVS). In 5 cases, the digital examination erroneously perceived an occiput posterior position as occiput anterior. No significant differences in fetal head position were detected between TUS and TVS, when the examination was technically feasible. The mean time (+/-SD) required for determining fetal head position was shortest for TVS (8.7 +/- 5.8 seconds) in comparison to DVE (22.7 +/- 14.6 seconds; P < .0001) or TAS (31.7 +/- 19.1 seconds; P < .0001).

Conclusion: Transvaginal sonography was the most successful and accurate method for determination of fetal head position in the second stage of labor, and required the least time for performance. We believe that TVS should be routinely performed in the labor room setting for the determination of fetal head position.