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

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. Synopsis The contents of this page will be used as part of issue TOC only. It will not be published as part of main article. Measurement of HPD before OVD was not found to be predictive of the occurrence of an OASIS.