Objectives This paper reviews the causes anal sphincter injury during vaginal delivery. It emphasises that they are not usually the result of poor obstetric care. The role of the colorectal surgeon in their management is discussed.
Methods Medline was searched using the key words third degree tears, pregnancy, risk factors, prevention and recurrence risk. A hand search of journals and located articles was made. Two hundred and twenty three papers were identified, 84 are referenced.
Results The reported incidence of anal sphincter tears is usually between 0.5% and 2.5% of vaginal deliveries. Maternal factors such as parity and age and obstetric factors such as mode of presentation, the use of forceps and the size of the baby all influence the incidence of sphincter tears. Predicting tears in individual women is inaccurate and midwifery practices can do little to prevent them. Reducing pelvic floor morbidity by increasing the caesarean section rate would require that a large number of caesarean sections be done to prevent a small number of tears. The recognition of perineal trauma is improved by training. Accurate apposition of the sphincters with antibiotic cover and post-operative laxatives are the important technical aspects of the repair. Colorectal follow up helps to identify those women with symptoms and allows advice about the advisability of subsequent vaginal deliveries. A previous third degree tears increases the risk of a subsequent one, although the overall risk remains low. A second vaginal delivery after a third degree tear that has resulted in a functional deficit predisposes to worsening function. When there is no residual anatomical defect and no functional loss, there is no evidence of increased risk of incontinence following another vaginal delivery.
Conclusion Vaginal delivery will continue to be the main method of delivery and will continue to generate a low incidence of pelvic floor morbidity. The management of injury to the anal sphincter is facilitated by close co-operation between obstetricians and colorectal surgeons.