From the Guidelines
The four features of delivery that increase the risk of sphincter damage are forceps-assisted delivery, prolonged second stage of labor, large fetal size (macrosomia), and occipito-posterior position of the fetus. These features are associated with a higher risk of obstetrical anal sphincter injury (OASIS) due to various mechanisms, including direct trauma, tissue fatigue, and increased mechanical stress on perineal tissues 1. Key factors contributing to this risk include:
- Forceps delivery, which can directly traumatize the anal sphincter complex
- Prolonged second stage of labor, causing tissue fatigue and reduced elasticity
- Macrosomia, creating mechanical stress on perineal tissues due to increased stretching required for passage
- Occipito-posterior position, presenting a larger diameter of the fetal head to the perineum and increasing pressure on the sphincter mechanism Recognizing these risk factors is crucial for clinicians to consider preventive measures, such as mediolateral episiotomy in high-risk situations or modified delivery techniques, to reduce sphincter trauma and subsequent morbidity, including anal incontinence and chronic pain 1.
From the Research
Features of Delivery that Increase Risk of Sphincter Damage
The following features of delivery have been identified as increasing the risk of sphincter damage:
- Instrumental delivery, such as forceps or vacuum extraction 2, 3, 4, 5
- Prolonged second stage of labor, with each hourly increase associated with an increased risk of obstetric anal sphincter injury 4, 6
- Episiotomy, particularly when combined with forceps delivery 3, 5, 6
- Epidural anesthesia, which can prolong the second stage of labor and increase the risk of sphincter injury 4, 5
Additional Risk Factors
Other risk factors that may contribute to sphincter damage include: