Predictive factors for obstetric anal sphincter injury in primiparous women: systematic review and meta‐analysis

Abstract

ObjectivesThe primary objective was to perform a systematic review on predictive factors for Obstetric Anal Sphincter Injury (OASI) occurrence at a first vaginal delivery, where the diagnosis was made by ultrasound (US‐OASI). The secondary objective was to report on incidence rates of sonographic AS trauma, including trauma that was not clinically reported on at childbirth, among the studies providing data for our primary endpoint.MethodsWe conducted a systematic search of MEDLINE, Embase, Web of Science, Cinahl, Cochrane library and Clinicaltrials.gov databases. Both observational cohort studies and interventional trials were eligible for inclusion. Study eligibility was assessed independently by two authors. Random‐effect meta‐analyses were performed to pool effect estimates from studies reporting on similar predictive factors. Summary Odds Ratios (ORs) or Mean Differences (MDs) were reported with 95% CI. Heterogeneity was assessed using the I2 statistic. Methodological quality was assessed using the Quality in Prognosis Studies tool.Results2805 records were screened and 21 met the inclusion criteria (16 prospective cohort, three retrospective cohort and two interventional non‐randomized trials). Increasing gestational age at delivery (MD 0.34w [0.04, 0.64]), shorter antepartum perineal body length (MD ‐0.60cm [‐1.09, ‐0.11]), labor augmentation (OR 1.81 [1.21‐2.71]), instrumental delivery (OR 2.13 [1.13‐4.01]), in particular forceps extraction (OR 3.56 [1.31‐9.67]), shoulder dystocia (OR 12.07 [1.06‐137.6]), episiotomy use (OR 1.85 [1.11‐3.06]) and shorter episiotomy length (MD ‐0.40cm [‐0.75, ‐0.05]) were associated with US‐OASI. When pooling incidence rates, 26% of women who first delivered vaginally, had sonographic evidence of AS trauma (95%CI 20‐32%, 20 studies, I2=88%). In studies reporting on both clinical and ultrasound OASI rates, 20% of women had AS trauma on ultrasound, that was not reported on at childbirth (95%CI 14‐28%, 16 studies, I2=90%). No differences were found in maternal age, BMI, weight, subpubic arch angle, induction of labor, epidural analgesia, duration of first/second/active second stage, vacuum extraction, neonatal birthweight or head circumference. Also, antenatal perineal massage and use of an intrapartum pelvic floor muscle dilator did not affect the odds of US‐OASI. Most studies (81%) were judged at high risk of bias on at least one domain, and only four studies (19%) had an overall low risk of bias.ConclusionGiven there was ultrasound evidence of structural damage to the AS in 26% of women who first delivered vaginally, clinicians should have a low threshold of suspicion. Our systematic review identified several predictive factors for this.This article is protected by copyright. All rights reserved.

Long-term effects of neuraxial analgesia

“…Obstetric anal sphincter injury, defined as a perineal tear extending into the anal sphincter complex, is a serious complication of childbirth and epidurals have been postulated as a potential risk factor. In a systematic review and meta-analysis of 16 studies, epidural analgesia was not found to be associated with anal sphincter injury whilst increased gestational age, labour augmentation, forceps delivery, episiotomy and shoulder dystocia increased the risk [30].…”

The pelvic floor during pregnancy and delivery: Can pelvic floor trauma and disorders be prevented?

“…Instrumental deliveries, and in particular forceps deliveries, in nulliparous women are associated with an increased risk of anal sphincter injuries 13 . Fetal position and station should be identified precisely before instrumental vaginal deliveries and change of instrument (eg vacuum converted to forceps) should be avoided.…”

“…Instrumental deliveries, and in particular forceps deliveries, in nulliparous women are associated with an increased risk of anal sphincter injuries. 13 Fetal position and station should be identified precisely before instrumental vaginal deliveries and change of instrument (eg vacuum converted to forceps) should be avoided. Instrumental delivery in the occiput posterior position has the highest risk of anal sphincter injuries, and knowledge about correct traction direction is important.…”