Is sonographic measurement of head-perineum distance useful to predict obstetrical anal sphincter injury in case of vacuum delivery?

ABSTRACT

OBJECTIVE: Determine if head-perineum distance (HPD) measurement before vacuum extraction (VE) was predictive of an obstetric anal sphincter injury (OASIS) occurrence. METHODS: Retrospective, bicentric (Lille and Poissy, France) cohort study conducted from January 2019 to June 2020. All VE in singleton pregnancies of ≥34 weeks were included. HPD measurement was performed without compression of the tissues before each VE. The judgment criterion was the occurrence of an OASIS. RESULTS: Of 12 568 deliveries, VE was performed in 1093 (8.6%). Among these 1093 women undergoing VE, 675 (61.7%) with HPD measurement were included. OASIS was found in 6.5% of women (n = 44; 95% CI 4.5-8.7). HPD was not associated with OASIS (38.5 ± 12.6 mm in women with OASIS vs 37.4 ± 12.0 mm in women without; adjusted OR [aOR] per 5 mm increase = 0.92; 95% CI 0.79-1.06). Increased HPD was associated with higher risk of sequential extraction (aOR = 1.19; 95% CI 1.06-1.32), extraction duration >10 min (aOR = 1.12; 95% CI 1.02-1.23) and shoulder dystocia (aOR = 1.20; 95% CI 1.03-1.40). CONCLUSION: Ultrasound-measured head-perineum distance does not predict the occurrence of obstetric anal sphincter injury during a VE. The interest of HPD is more about predicting the success or difficulty of VE rather its specific complications.