A study of progress of labour using intrapartum translabial ultrasound, assessing head station, direction, and angle of descent

OBJECTIVE: Intrapartum translabial ultrasound (ITU) has the potential to objectively and quantitatively assess the progress of labour. The relationships between the different ITU parameters and their development during normal term labour have not been studied. DESIGN: Observational study. SETTING: University teaching hospital. POPULATION: Labouring women with normal term fetuses in cephalic presentation. METHODS: Intrapartum translabial ultrasound measurements for 'head station', 'head direction', and 'angle of descent' (AoD) were taken in 50 labouring women, compared, studied for repeatability, and correlated with the progress of labour. MAIN OUTCOME MEASURES: Reproducibility and correlation of ITU parameters and their pattern of changes during labour. RESULTS: All three ITU parameters were clinically well reproducible. AoD and head station were interchangeable, and could be calculated from each other. Head station and head direction changed in a typical pattern along the birth canal. Time to delivery correlated with ITU head station. CONCLUSIONS: Intrapartum translabial ultrasound is a simple technique that improves the understanding of normal and abnormal labour, enables the objective measurement of birth progress and provides a more scientific basis for assessing labour.