Background: Prediction of the mode of delivery is crucial for better labour outcome.
Recent studies suggest that the angle of progression (AOP), measured using transperineal ultrasound,
can substantially aid the assessment of fetal head descent during labor, thereby predicting
the mode of delivery.
Objective: To assess the ability of the AOP measured by transperineal ultrasound to predict the
mode of delivery in nulliparous women before the onset of labor.
Methods: A prospective observational study was conducted at our hospital, of nulliparous women
who had presented to the antenatal clinic at ≥ 38 weeks of gestation but not in labor. AOP was
measured using transperineal ultrasonography and compared among the women having Caesarean
section (CS) due to labor dystocia and vaginal delivery (VD). Various other confounding factors
which increase the risk of caesarean section were analyzed.
Results: Among total 120 nulliparous women, the mean AOP was narrower in patients undergoing
CS (n = 28) compared to those with VD (n = 92) (91.6 ± 6.1° vs. 100.7 ± 6.9°; P < 0.01). Multivariable
logistic regression analysis revealed that narrow AOP values (OR 3.66; P < 0.001; 95% CI 1.7-
14.5) and occiput-posterior fetal position (OR 1.63; P = 0.04; 95% CI 1.0-7.5) were the independent
risk factors for CS. An AOP ≥ 96° (calculated from the ROC curve) was associated with VD in
95% (76/80) of women and an AOP < 96° was observed among 60% (24/40) of women who underwent
Conclusion: Narrow AOP (< 96°) and occiput-posterior fetal position are at higher risk for CS due
to labor dystocia. AOP measured at the antenatal period could accurately predict the mode of delivery,
thereby modifying labor outcome.