Risk factors for perineal trauma in the primiparous population during non-operative vaginal delivery.

INTRODUCTION AND HYPOTHESIS: Obstetric anal sphincter injuries (OASIS) are more common in the primiparous population, especially during operative vaginal delivery (OVD). It would therefore be interesting to establish what factors influence the risk of OASIS when adjusting for the risk bias of OVD. METHODS: Retrospective analysis of prospectively collected data from the maternity database at University of Southampton NHS Foundation Trust of primiparous women sustaining OASIS during a singleton, term, cephalic, non-operative vaginal delivery between 2004 and 2015. A control comparison was made of women with otherwise identical birthing conditions but resulting with intact perinea, delivering between 2014 and 2015. Univariate and multivariate logistic regression compared maternal, intrapartum and neonatal factors of those sustaining OASIS with those with an intact perineum. RESULTS: Seven hundred fifty-six women sustaining an OASI met the criteria, and comparisons were made with a control population of 212. Those sustaining an OASI were significantly older (p < 0.001), more likely to be Asian (4.6-fold, p < 0.001) and had heavier babies, with a 3.6-fold greater proportion over 4 kg (p = 0.001). They were more likely to have delivered post-term and had longer second stages of labour (both p < 0.001). Epidural anaesthesia was associated with a 67% reduction in OASIS. CONCLUSIONS: These findings support previous research regarding risk factors for OASIS. By controlling for bias of risk associated with operative vaginal delivery, this revealed a potential protective effect of the use of regional anaesthesia.

Risk factors for obstetric anal sphincter injuries at vaginal birth after caesarean: a retrospective cohort study.

INTRODUCTION AND HYPOTHESIS: Vaginal birth after caesarean (VBAC) is associated with an increased risk of obstetric anal sphincter injuries (OASIS). However, specific factors that influence the risk of OASIS at VBAC have not been studied, particularly whether there are specific baseline characteristics of the first delivery which affect the subsequent perineal outcomes. METHODS: Retrospective analysis of prospectively collected data from University of Southampton NHS Foundation Trusts' maternity database. This included secundiparous women with a previous caesarean delivery (CS) who achieved a singleton, term, cephalic vaginal delivery from 2004 to 2014. Univariate analysis compared maternal, intrapartum and neonatal factors of those who suffered OASIS at VBAC with those who did not. A binary logistic regression model calculated the adjusted, independent odds ratio (OR) of OASIS. RESULTS: A total of 1375 women met the inclusion criteria. The OASIS rate was 8.1%, a 1.4-fold increase compared with primiparous women [difference 2.4% (95% CI 1.1, 3.6)]. Those sustaining OASIS at VBAC were older (p = 0.011) and had infants of greater birth weight at initial caesarean (p < 0.001) and VBAC (p = 0.04). Analysis of odds ratios revealed that mediolateral episiotomy (MLE) at VBAC halved the risk of OASIS [37.5% VBAC with OASIS vs. 52.2% VBAC without OASIS (OR 0.51, 95% CI 0.32-0.81)], whereas an urgent CS at initial delivery doubled the risk [52.3% VBAC with OASIS vs. 34.9% VBAC without OASIS (OR 2.05, 95% CI 1.31-3.21)]. CONCLUSIONS: Advanced maternal age, increased infant birth weight and an urgent category of initial CS increase the risk of OASIS at VBAC, whereas MLE is protective.