In humans and some other primates, the head of the term fetus is so large in comparison to the size of the birth canal that delivery may result in some degree of trauma. As the head passes through the pelvis, the soft tissues are stretched and compressed. The risk of severe<unk>  is greatly increased if the fetal head is oriented occiput posterior (face forward), if the mother has not given birth before or if the fetus is large. A surgical incision on the perineum skin called an episiotomy was historically used routinely in order to reduce<unk> s. However, its routine use has declined as there is some evidence it increases the severity of<unk> s when it is not indicated. A Cochrane review found that routine use of episiotomy increased the incidence of severe<unk> s by 30%. Several other techniques are used to reduce the risk of<unk> ing, but with little evidence for efficacy. Antenatal digital<unk>  massage is often advocated, and may reduce the risk of trauma only in nulliparous women. ‘Hands on’ techniques employed by midwives, in which the foetal head is guided through the vagina at a controlled rate have been widely advocated, but their efficacy is unclear. Waterbirth and labouring in water are popular for several reasons, and it has been suggested that by softening the perineum they might reduce the rate of<unk> ing. However, this effect has never been clearly demonstrated.
Perineal tear
Perineal hernia
Perianal hematoma
Rectovaginal fistula
Retroperitoneal fibrosis
Vesicovaginal fistula
Sigmoidocele
Urethrovaginal fistula