Comparison between ultrasound parameters and clinical examination to assess fetal head station in labor

Several ultrasound parameters, including intrapartum transperineal ultrasound (ITU) head station, angle of progression (AOP), head-perineum distance (HPD) and head-symphysis distance (HSD), have been suggested to assess fetal head station during labor. The aim of this study was to analyze the relationship between these ultrasound parameters and to compare them with digital palpation.

We analyzed 106 stored volume dataset pairs that had been acquired at Stavanger University Hospital, Norway, from nulliparous women at term with prolonged first stage of labor. The volumes were acquired using a three-dimensional transducer applied between the labia majora in a mid-sagittal plane and perineally in a transverse plane. Digitally palpated head station and cervical dilatation were also noted. The results were compared using regression and correlation coefficients.

There were good correlations between ITU head station and HPD (r = 0.71), between ITU head station and HSD (r = 0.74) and between HSD and HPD (r = 0.75). Palpated head station showed only moderate correlation with ITU head station (r = 0.52). Cervical dilatation showed a weak correlation with ITU head station (r = 0.30).

The ultrasound parameters showed a high degree of correlation with each other, but only moderate correlation to vaginally palpated fetal head station.