One of the critical stages during labour is when the baby’s head passes down the birth canal and into the outside world. The head is large and the tissues surrounding the outlets of the vagina and rectum, called the perineum, must stretch considerably to allow its passage. In most deliveries the perineal muscles and skin are elastic enough and, if the head emerges slowly and well-flexed, there is little if any damage to the area. However if the head is proportionally large, or the perineum tight or inflexible – especially in a first delivery – there is a risk of the perineum tearing. To prevent this it may be advisable for the perineal tissue to be carefully cut, to enlarge the opening. This cut is called an episiotomy.

The advantages of a well-timed episiotomy over a perineal tear are that damage to the rectum is unlikely to develop, and that the baby’s head is under less pressure during delivery, because the opening is wider. And because overstretching of the vaginal muscles is avoided, this may help to prevent vaginal prolapse in later life. Although the surgical cut of an episiotomy is not as ragged as a tear and is less difficult to repair, it generally does not heal as quickly. There is some evidence that subsequent sexual problems (such as pain during intercourse) are less likely to develop after a tear. That is why some obstetricians prefer the risk of a minor tear to a too exaggerated use of episiotomy.

Most commonly the cut is made from the middle of the posterior wall of the vaginal opening in a diagonal direction, to the right or left. This is termed a mediolateral episiotomy. The reason for a diagonal cut is that, if there is tearing despite the episiotomy, it is unlikely to damage the rectum, which is difficult to repair. Before making the cut a local anaesthetic is injected, usually at the height of a contraction so that the mother is least likely to feel it.

Following delivery of the baby and placenta the episiotomy is sown up. Firstly the vaginal wall is repaired, then the muscles of the perineum, and finally the skin. Often the area is still numb from the local anaesthetic, but if sensation has returned another injection may be advised. At an early postnatal check-up the area is examined and the remaining stitches removed as necessary.

Episiotomies have been performed almost as routine in some areas during recent years, particularly for first deliveries. However, as mentioned above, attitudes are changing. With a little extra time and care many episiotomies can be avoided. The discomfort they cause may have been underestimated by some obstetricians, especially as occasionally an incision becomes infected and takes several weeks to heal.