480 Intrapartum sonographic features of cephalopelvic disproportion in non-occiput posterior fetuses: prospective multicenter study

Abstract

To describe the intrapartum sonographic characteristics of cephalopelvic disproportion (CPD) in labor arrest in non-occiput posterior (OP) position. Prospective study conducted across three tertiary maternity Units and including women with prolonged first stage of labor and fetuses lying in non-OP position. In the recruited cases transabdominal ultrasound was performed in order to evaluate the degree of flection of the fetal head by means of the occiput-spine angle (OSA), while the sonographic indicators of head station – i.e. the angle-of-progression (AoP) and the head-perineum distance (HPD) – and additional signs of CPD were assessed at transperineal ultrasound. Obstetric intervention performed solely based on suspected fetal distress represented exclusion criteria for the study. Overall, 86 women were included. Spontaneous vaginal delivery, instrumental delivery and cesarean section were recorded in 45 (52.3%), 11 (12.8%) and 30 (34.9%) cases, respectively. A wider OSA (126.2+14.4 vs 114.5+23.6 degrees, p=0.006) and AoP (117.5+12.7 vs 104.0+10.7 degrees, p<0.001) and a shorter HPD (39.7+5.2 vs 49.0+9.4 mm, p<0.001) were measured in women who had vaginal delivery compared to those delivered by cesarean section. When investigating the correlation between the OSA and the sonographic indices of head station, the OSA showed a direct correlation with the AoP (Pearson’s correlation 0.449, p<0.01) but no correlation with the HPD (p=0.15); 9 cases showing a narrow AoP, a long HPD and a wide OSA and all delivered by cesarean section were labelled as outliers. Such cases showed a lower maternal height (p<0.01) and a higher ratio between the birthweight and the maternal height (p=0.04) compared to the non-outlier cases. Caput succedaneum and moulding were also noted at transperineal ultrasound in all the outlier cases. Findings from this study suggest that a discrepancy between the width of the OSA and the expected AoP and HPD represent sonographic indicators of CPD in non-OP fetuses diagnosed with labor arrest.