Use of a hysterometer to measure the head–perineum distance before an operative delivery: a prospective study

Introduction: Many studies have investigated the contribution of transperineal ultrasound in determining the fetal head station during the management of the second stage of delivery. The head–perineum distance (HPD) remains 1 of the most studied measures.We hypothesized that a HPD measured “clinically” with a hysterometer might correlate with that measured by transperineal ultrasound and could be used to predict the risk of cesarean delivery. STUDY DESIGN: This was a unicentric prospective observational study that occurred between February 10, 2022, and June 30, 2024. Women with a singleton fetus in the cephalic presentation at term (≥37 weeks of gestation) who had an operative delivery (vaginal operative birth or cesarean delivery during the second stage) were eligible for this study. Women were included during the second stage if an operative delivery was expected. The HPD was measured using 2 devices: transperineal ultrasound (HPDus) and a hysterometer (HPDhys). Correlations and agreement were calculated, and receiver-operating characteristic curve analysis was conducted to evaluate the performance of each method in predicting cesarean delivery. RESULTS The final population comprised 671 women who underwent both HPDhys and HPDus. Pearson correlational analysis showed good agreement between both methods: r  = .85 (95% confidence interval [CI] .84–.88). Correlations were independent of the level of the fetus head station and head position. The area-under-the-curve values were high for both methods: 0.87 (95% CI 82.8–92.1) for clinical HPDhys and 0.83 (95% CI 0.78–0.89) for HPDus ( P  = .006). CONCLUSIONS HPD measured with a hysterometer is accessible to all practitioners and correlates well with HPD measured with transperineal ultrasound. HPD has potential as a tool to help clinicians select the appropriate indications for instrumental deliveries. It is hoped that this easily accessible technique will be used widely, especially in countries where ultrasound resources may be limited. Further studies are needed to confirm the results of this study.