OP19.10: Transperineal ultrasound to assess fetal head station in labour: a more objective assessment of labour?

Abstract

Head station is a particularly subjective assessment of labour progress. We assessed the feasibility of using intrapartum transperineal ultrasound (US) as an objective, non-invasive measure of head station by determining the agreement with VE, the proportion of stations measurable on US and the effect of caput. 196 women recruited at a tertiary London maternity unit 2015-17. Paired measures (<30 mins apart) of head station were taken during labour using digital VE (WHO criteria) and transperineal US measured head-perineum distance (HPD). The proportion of stations measurable on US and VE were assessed. Paired measures were compared by linear regression and correlation to determine agreement, a one-way ANOVA was performed to determine if mean HPD differed significantly between stations on VE. The relationship between US measures of caput vs. VE measurement of station was explored. Of 318 assessments recorded, 12 (3.8%) stations were not recorded on VE and 14 (4.4%) HPD were not determined on US (p=0.69). 217 assessments were analysed (76 assessments were excluded from analysis because the US and VE were performed >30mins apart). Station and HPD were negatively correlated (Spearman's r=-0.576, p<0.0001). 1- way ANOVA showed significant differences in mean HPD between stations of -2/-1 and -1/0 (p<0.05 and p<0.0001 respectively). Taking HPD as the distance to fetal scalp rather than skull (to account for caput), the relationship between HPD and station on VE became stronger (linear regression -5.33 ± 0.484 to -8.59 ± 0.769, p=0.0004). Agreement between HPD and VE for head station is poor with a large variation in VE measured head station compared to US measured HPD, indicating VE is imprecise. Caput significantly influences the clinicians understanding of head station.