Emerging role of angle of progression and head-perineum distance in predicting labor outcome: original research supported by a mini-review

Background : Intrapartum ultrasound (ITU) has garnered significant attention in recent years. While its use is well-documented in developed countries, it has not yet gained popularity in under- resourced countries. Despite the widespread availability of ultrasound (US) in most labor and delivery centers, its use is predominantly limited to identifying obstetric emergencies, with minimal application in assessing labor progress. The use of ITU has not been sufficiently tested in labor and delivery settings within developing countries. Aim : To evaluate the diagnostic performance of ITU parameters of 1. Angle of progression (AOP) and 2. Head perineum distance (HPD) in predicting a vaginal delivery in term singleton pregnant women in early labor and to provide a comprehensive review of literature. Methods : Prospective observational study conducted in South India. Singleton pregnant women over 37 weeks of gestation in early labor were included. AOP and HPD were measured using trans-perineal ultrasound in addition to clinical vaginal assessment. Two trained obstetricians performed the ultrasound examination on initial 22 women. ITU measurements were analysed to identify the best possible predictive value for the outcome vaginal delivery. Results : Among 113 parturients, the mean AOP was narrower in women who underwent Caesarean CD (27%, n= 31), compared to those who has a vaginal delivery (VD), (72.5%, n=82). An AOP > 104.5° was predictive of VD with a sensitivity 94% and specificity 95%. HPD of ≤39.5mm was predictive of VD with a sensitivity 64% and specificity 65%. Conclusion : Measuring AOP and HPD during labor provides valuable insights into the likelihood of a vaginal delivery with AOP being a more reliable indicator than HPD. Implementing the use of these measurements in labor management could empower obstetricians to confidently await a vaginal delivery, particularly in situations where labor duration exceeds the expected timeframe, while maternal and fetal conditions are satisfactory. Trial Registration: Reg No. CTRI/2021/02/030936, Reg Date: 02.02.2021, URL: www.ctri.nic.in