Serial intrapartum ultrasound to predict vaginal delivery using angle of progression and head- progression distance in term nulliparous women.

Introduction: Over the past decade, intrapartum ultrasound (ITU) has been in the global limelight for labour monitoring. The use of the same in clinical settings of low- and middle-income countries (LMIC's) however, is limited. Till date, angle of progression (AOP) stands as the most studied parameter. Very few studies, most from developed countries, have shown that other ITU measurements could also hold relevance to labour and delivery. In recent times, serial ITU has also garnered some attention and could possibly be a better predictor of labour outcome.

Aims: This study aimed to compare the predictive accuracies of AOP and head PD for vaginal delivery and to investigate whether the rate of change of serially measured AOP and head PD in the first stage is predictive of vaginal delivery.

Methods: A prospective observational study was conducted on 90 nulliparous women between April 2023 and July 2024 at a tertiary teaching hospital in South India. Participants had singleton pregnancies in cephalic presentation between 37-40 weeks with regular contractions, and cervical dilation ≥ 3 cm. Exclusion criteria included prior LSCS and abnormal cardiotocography. Intrapartum ultrasound was performed twice, once at recruitment and 3-5 h apart, to measure AOP and PD. Statistical analysis included ROC curve plotting for diagnostic accuracy of AOP and PD in predicting vaginal delivery.

Results: Of the 90 participants, 71 (78.9 %) delivered vaginally and 19 (21.1 %) had caesarean sections. AOP ≥ 120° and PD ≥ 2.7 cm at ≥ 6 cm cervical dilation showed a strong correlation with vaginal delivery, with sensitivity and specificity of 70.4 % and 94.7 %, and 63.4 % and 89.5 % respectively. Change (delta) in AOP > 10° had the highest diagnostic accuracy (81 %), with a positive predictive value of 92.2 %.

Conclusion: ITU offers valuable insights into labour progression. AOP and PD, particularly at cervical dilation of ≥ 6 cm, are predictive of vaginal delivery. Delta AOP serves as the most accurate predictor. Incorporating ITU into routine labour management enhances clinical decision-making, helping reduce unnecessary interventions and caesarean deliveries.