The head direction to the angle of progression ratio: a quantitative parameter for intrapartum evaluation of cephalic malposition.

Background: No previous study has evaluated the transitions of intrapartum transperineal ultrasound parameters during labor progression in cephalic malposition.

Objective: We aimed to quantitate the characteristic trends of fetal head position and descent in cephalic malposition by analyzing the transitions of intrapartum transperineal ultrasound parameters and explore an indicator associated with the degree of cephalic malposition.

Study Design: We retrospectively analyzed pregnant women who delivered at term from January 2018 to December 2020 at the University of Tokyo Hospital.