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Predictors and Unexplained Variability of Obstetric Anal Sphincter Injuries: A Population-Based Cross-Sectional
Christopher X Hong1, Pamela S Fairchild2, Payton C Schmidt2
1Department of Obstetrics and Gynecology, University of Michigan, University Hospital South, 1500 E. Medical Center Dr., L4011, Ann Arbor, MI, 48109, USA. cxhong@med.umich.edu.
International Urogynecology Journal
|November 1, 2024
Summary
Obstetric anal sphincter injuries (OASIs) occur in 1.1% of vaginal births. Vaginal parity and operative birth are the strongest clinical predictors, but most OASI cases remain unexplained by these factors.
Area of Science:
- Obstetrics and Gynecology
- Maternal-Fetal Medicine
- Epidemiology
Background:
- Obstetric anal sphincter injuries (OASIs) are a significant concern in childbirth.
- Understanding the incidence and risk factors for OASIs is crucial for improving maternal outcomes.
- Existing literature suggests several clinical factors may influence OASI risk.
Purpose of the Study:
- To determine the incidence of OASIs in a US population.
- To assess the predictive power of individual and collective clinical risk factors for OASIs.
- To identify key predictors of OASIs using a large birth registry.
Main Methods:
- A cross-sectional study utilizing US National Vital Statistics System data (2016-2021).
- Inclusion of all vaginal births, excluding those with unspecified delivery route or perineal laceration status.
- Logistic regression models and pseudo-R-squared (pR2) values to evaluate the predictive strength of clinical risk factors.
Main Results:
- Analyzed 15,413,957 vaginal births; overall OASI incidence was 1.1%.
- Vaginal parity (pR2 5.8%) and operative birth (pR2 4.8%) were the most predictive factors for OASIs.
- Infant weight showed moderate predictive capability (pR2 1.5%), while other factors had minimal predictive power (pR2 ≤ 0.5%).
- The multivariable model explained 11.8% of OASI variability.
Conclusions:
- Vaginal parity and operative birth are significant clinical predictors of OASIs, each contributing approximately 5% to outcome variation.
- A substantial proportion of OASIs are not explained by current clinical risk factors.
- Further research into OASI mechanisms is needed to develop targeted interventions and identify high-risk individuals.
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