Relationship between intrapartum transperineal ultrasound measurement of angle of progression and head-perineum distance with correlation to conventional clinical parameters of labor progress and time to delivery

Objective: To assess whether angle of progression (AOP) and head-perineum distance (HPD) measured by intrapartum transperineal ultrasound (ITU) correlate with clinical fetal head station (station); and whether AOP versus HPD varies during uterine contraction and relaxation. In a subset of primipaorus women, whether these ITU parameters correlate with time to normal spontaneous delivery (TD). Methods: We evaluated prospectively 100 primiparous and multiparous women at term in active labor. Transabdominal and transperineal ultrasound (sagittal and transverse plane) were used to measure fetal head position and ITU parameters, respectively. Digitally palpated station and cervical dilatation were also noted. The results were compared using regression and correlation coefficients. Results: Station was moderately correlated with AOP (r = 0.579) and HPD (r = -0.497). AOP was highly correlated with HPD during uterine contraction (r = -0.703) and relaxation (r = -0.647). In the subgroup of primiparous women, natural log of TD has the highest correlation with HPD and AOP during uterine contraction (r = 0.742), making prediction of TD similar to that of using cervical dilatation. Conclusion: ITU parameters were moderately correlated with station. There was constant high correlation between AOP and HPD. Prediction of TD in primiparous women using ITU parameters was similar to that of using cervical dilatation.