Fetal head-symphysis distance: a simple and reliable ultrasound parameter for the intrapartum assessment of the fetal head descent

OP18.05 Fetal head-symphysis distance: a simple and reliable ultrasound parameter for the intrapartum assessment of the fetal head descent A. Youssef, E. Maroni, F. De Musso, A. Ragusa, G. Salsi, F. Bellussi, M. Nanni, N. Rizzo, G. Pilu, T. Ghi Obstetrics and Gynecology, University of Bologna, Bologna, Italy Objectives: to introduce the fetal head-symphysis pubis distance (HSD) as a novel sonographic parameter for the assessment of fetal head station in labor; to assess its repeatability using threedimensional ultrasound (3DUS) and to evaluate its correlation with digital examination. Methods: A series of 47 US volumes was translabially acquired from nulliparous women in active labor after digital examination and stored for offline analysis. HSD (distance between the lower border symphysis pubis and the nearest point of the fetal skull along a line passing perpendicular to the long axis of SP and tangential to its lower border) was measured in the midsagittal plane by two operators blinded to the results of clinical evaluation. Angle of progression was also measured in each volume dataset. Intra- and interobserver repeatability for HSD was determined. Lastly, HSD was measured on the left and right parasagittal planes. Regression analysis was used to estimate the correlation between HSD with the fetal head station at digital examination and AoP. Results: HSD showed high intra- and inter-observer repeatability (see table). HSD showed significant correlation with digital examination (Spearman rank correlation coefficient −0.918) and with angle of progression (Pearson correlation coefficient (r) = −0.826). Furthermore, HSD showed a high repeatability on parasagittal measurements. Conclusions: Fetal head-symphysis pubis distance is a new simple and reliable sonographic parameter for the assessment of fetal head descent in labor.