Trends and predictors of obstetric anal sphincter injury at childbirth

Abstract

Aims Aims of this PhD study were to: examine temporal trends in obstetric anal sphincter injury (OASI) in New South Wales (NSW) Australia, and associated risk factors; determine recurrence risk; evaluate the impact of data sources; and identify perineal support practices used by midwives. Methods Analysis of linked NSW population-based administrative data (NSW Perinatal Data Collection [‘birth data’] and the Admitted Patient Data Collection [‘hospital data’]) was undertaken using logistic regression, predictive modelling and agreement statistics. Midwifery practice was investigated by cross-sectional survey and descriptive analysis. Results Vaginal OASI rates rose from 2.2% (2001) to 3.3% (2011), with significant increases among women having a non-instrumental birth or forceps birth with episiotomy. Risk factors included primiparity, instrumental births, Asian maternal country of birth and high birthweight, but changes in their prevalence did not explain OASI increase. Recurrence risk was 5.7%. OASI ascertainment was higher using hospital data. Midwives preferred a ‘hands poised’ approach. Conclusions These results can help inform clinical decisions and highlight both the importance of using linked hospital data in OASI research, and the need for ongoing research to identify drivers of increased OASI risk.