The need for perineal repair after childbirth affects millions of women worldwide. In the United Kingdom, approximately 85% of women sustain some form of perineal trauma during vaginal delivery, and 69% of these will require stitches. It is difficult to gauge the true prevalence of perineal trauma, owing to variation in obstetric practice globally. There is considerable variation in the reported national as well as international rates of obstetric anal sphincter injury (OASI). In the UK, the overall mean reported national rate of OASI is 2.9% (range 0–8%), and 6% (range 0–15%) of women having their first vaginal delivery will sustain an OASI. Similar variations in the incidence of OASIs have also been noted in the 22 Organisation for Economic Cooperation and Development (OECD) countries: 1.6% (range 1–3.7%) with normal vaginal deliveries and 6% (range 1–17%) with instrumental deliveries.
There is evidence that the OASI rate is rising globally, and in England the rate tripled from 1.8% to 5.9% between the years 2000 and 2012. This observation has raised concern, and it has been suggested that OASI rates should be a performance indicator and a measure of obstetric quality outcomes. The reason for this is that it has been shown in one study that a number of OASIs believed to be “occult” (only seen by endoanal ultrasound) were in fact clinically missed OASIs. While the rising OASI rate has been attributed to improvements in training and diagnosis, there is also emerging concern that there may be an element of overdiagnosis. Hands-on workshops using models, animal tissue, and audiovisual aids have been shown to be effective in improving knowledge, recognition of the full extent of the injury, better classification, and improvements in repair techniques.
Until recently, the concept of pelvic floor trauma was confined largely to perineal, vaginal, and anal sphincter injuries. However, in recent years, with advances in magnetic resonance imaging (MRI) and three-dimensional ultrasound, it has become evident that levator ani muscle (LAM) injuries form an important component of pelvic floor trauma. During vaginal delivery the LAM has to stretch up to 3.3 times its initial length to enable the fetus to pass through the pelvis.