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

Abstract

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.

Quantification of fetal head direction and descent

“…The value of this conversion was recently appreciated in another article in UOG 4 . The angle of descent is also easy to obtain and is reproducible 3,5 . We suggest using the parameter 'head direction' -in addition to head station -as we initially described it, because it enables a simple assessment 'at a glance'.…”

“…In a recent study 3 , we showed that head direction and the dynamics of head descent during a contraction and over the course of delivery depend on the absolute head station: at higher stations, head direction tends to be 'horizontal' or even 'down', but at ITU-measured head stations of 0 to +2, a marked upward change in direction occurs during a contraction (see videos S1 and S2 in Tutschek et al 3 ). Head station is measured as shown in Figure 1.…”

“…As well as head station and head descent, we proposed the 'head direction' as a simple measurement 2,3 (Figure 1). This was based on data from a pilot study obtained during the first and second stages of normal labor as well as immediately prior to operative vaginal delivery.…”

“…For clarification, the measurement of ITU head station requires two steps (Figure 1): (1) measuring the angle defined by two easily obtainable axes (pubic axis and head direction); (2) measuring the distance from the intersection of the head direction and the infrapubic line to the deepest bony part of the skull 3 . ITU head station is an objective measurement, expressed on the same scale with regard to the ischial spines as is the classical digital palpation.…”

Intrapartum Ultrasonography for Prediction of Vaginal Delivery: Review

“…1 Further understanding of the complex physiology of childbirth is possible due to intrapartum ultrasonography. It has been shown to provide objective information on the dynamics of different stages of labor.…”