Risk factors for obstetric anal sphincter injury after a successful multicentre interventional programme

Area of Science:

• Obstetrics and Gynecology
• Maternal-Fetal Medicine
• Surgical Safety

Background:

• Obstetric anal sphincter injuries (OASIS) represent a significant complication of vaginal delivery.
• A previous interventional program successfully reduced the overall OASIS rate from 4.6% to 2.0%.
• Understanding the risk profile associated with OASIS after such interventions is crucial for clinical practice.

Purpose of the Study:

• To evaluate and compare the risk profile of sustaining OASIS in different risk groups post-intervention.
• To assess the impact of an intervention focused on manual assistance during the second stage of labor on OASIS rates.
• To identify changes in the association between known risk factors and OASIS following the intervention.

Main Methods:

• A multicenter, interventional cohort study with a before-and-after comparison design.
• Data from 40,154 vaginal deliveries across four Norwegian obstetric departments between 2003 and 2009 were analyzed.
• Logistic regression was used to estimate odds ratios for OASIS associated with various risk factors pre- and post-intervention.

Main Results:

• The overall risk of OASIS decreased by 59% (OR 0.41) following the intervention.
• The most significant reduction in OASIS (65%) was observed in the low-risk group (Group 0).
• Established risk factors for OASIS, such as first vaginal delivery, high birthweight, forceps delivery, and mediolateral episiotomy, showed largely unchanged associations post-intervention.

Conclusions:

• The interventional program significantly reduced OASIS rates, with the greatest impact seen in low-risk births.
• Despite the overall reduction, the primary risk factors associated with OASIS remained consistent.
• Manual assistance during the second stage of labor appears effective in mitigating OASIS, particularly in lower-risk populations.