Sonographic features of cephalopelvic disproportion in labour arrest in occiput anterior fetuses: insights from a prospective multicentre study.

Objectives Cephalopelvic disproportion is a risk factor for arrest of labor and cesarean delivery. However, to date there are no reliable ways to diagnose it. The purpose of this study is to describe the sonographic features of cephalopelvic disproportion (CPD) in women with prolonged active phase of labour and fetuses in occiput anterior (OA) position.

Methods Prospective observational study conducted across three tertiary maternity units. Women with singleton term pregnancies, occiput anterior position of the fetal head and protracted active phase of labor were included. Cases were submitted to transabdominal ultrasound for the evaluation of the fetal head flexion, measured by means of the occiput-spine angle (OSA), and to transperineal ultrasound for the evaluation of the fetal head station, by means of the angle-of-progression (AoP) and the head-perineum distance (HPD). Cases where cesarean delivery (CS) was performed solely based on suspected fetal distress were excluded.

Results Overall, 59 women were included. SVD, VE and CS were recorded in 31 (52.5%), 10 (17.0%) and 22 (37.3%) cases, respectively. A direct correlation between the OSA and the AoP was demonstrated (p<0.01) but not for HPD (p=0.15). For both correlations, the distribution in relation to the mode of delivery identified 9 outlier cases delivered by CS, in which the values of the AoP and of the HPD were not consisted with the expected OSA. At paired comparison, a wider OSA (139.7±9.7 vs. 118.0±19.4, p<0.01) together with a longer HPD (56.4±6.0 vs. 41.8±6.4, p<0.01) and a narrower AoP (99.7±9.5 vs. 114.3±15.1, p<0.01) were found in the outlier cases, which also showed a higher ratio between the birthweight and the maternal height (22.6±1.6 vs. 20.7±2.6, p=0.04) compared to non-outlier cases.

Fig. 1 Scatter/dot charts demonstrating the correlations between the occiput-spine angle (OSA) and the angle of progression (AoP) and head-perineum distance (HPD) in fetuses in an occiput anterior position.

Conclusions Findings from this study suggest that a discrepancy between the width of the OSA and the expected AoP and HPD represent sonographic indicators of cephalopelvic disproportion in OA-fetuses diagnosed with prolonged active phase of labour.

Publication History

Article published online:
26 November 2021