Epidemiology of perineal trauma

The incidence of perineal trauma varies greatly among different countries. A systematic review from 2008 reported incidences of anal sphincter tears of 0.5% in the United Kingdom, 2.5% in Denmark, and 7% in Canada (4).

An increased incidence of OASIS in recent years has been also noted in countries such as Finland, Canada, and China. A com­parison of the occurrence of OASIS in Finland took place between 1997-1999 and 2006-2007 (30). Between the two time periods a rise from 0.5% to 1.8% and 0.1% to 0.3% was shown in both primiparous and multiparous women respectively. A study comparing the inci­dence of OASIS in Sweden and Italy between June 2005 and October 2006 found that Swedish women had a 23 times higher risk than Italian women (31). The incidence was 9.2% in Swedish and 0.4% in Italian women. Gestational age, birth weight, instrumental de­livery, and duration of second stage of labour were accountable for the difference.

Data from Nova Scotia showed a twofold increase in OASIS over a 10-year period despite a decline in episiotomy use and instrumental deliveries (32). The number of women experiencing a prolonged second stage of labour increased, however, was not responsible for the twofold rise in severe perineal trauma. It was hypothesized that this increase was due to better recognition of OASIS. The incidence of OASIS in China appears low with an increasing trend.

In contrast to the previously mentioned studies, data from Norway report a decrease in incidence which halved from 4% in 2003-2005 to 1.9% in 2008-2010 (34). This reduction was attributed to a peri­neal protection training programme that was implemented after an observed increase in OASIS incidence. This programme included interventions such as slowing the delivery of the baby’s head, man­oeuvres aiming to lower the pressure on the perineum, instructing the women not to push, and training on episiotomy technique.

Management of childbirth in terms of episiotomy rates is also vari­able with figures of 13% in England, 8% in Netherlands, 25% in the United States, and as high as 99% in Eastern European countries (4).

Another factor that is greatly variable among countries is the number of homebirths with 60% in Netherlands planning to give birth at home (35), whereas in the United Kingdom, only 2.7% of births take place in the home setting (36). The rates of perineal trauma in the hospital setting appear higher even after controlling for instrumental delivery and epidural use (1).

Several explanations have been proposed for the universally in­creased OASIS incidence in recent years. Many have attributed this to improved diagnosis with emphasis on clinical examination, endoanal ultrasonography, and anal manometry as well as training programmes (37).

The limitation ofcomparisons between studies as inclusion criteria may differ impacting reported OASIS incidence has also been recog­nized (38). Another possible reason is the role of maternal age at first birth with many women delaying childbirth. This was supported by a study that demonstrated that levator trauma was increased by 10% for every year of delay of childbirth (39) as well as increased preva­lence of stress incontinence in delayed childbearing (40).

Faecal incontinence is common after OASIS, with a prevalence of 16-47% (41-44). Several studies have demonstrated a significant short- term risk of anal incontinence after OASIS (45, 46). The preva­lence of postnatal faecal incontinence symptoms 10 months after delivery was 4%. Flatal incontinence was reported in about 29% of women at 9 months after delivery (47).