Tearing of the tissue between vagina and anus, usually during the birth of the head, or less often the shoulders, of a baby during labour. The most important factors are a large baby, a narrow vagina or a baby driven out with great force at the last minute. The injury is assigned a degree of severity. In the first degree only the skin is torn, and may not even need to be stitched; in the second degree the underlying muscles and the vaginal wall are torn; in the third degree or total rupture the anal ring muscle is affected, and then stitching in hospital under general anaesthetic is required. Spontaneous rupture usually follows the central line in the direction of the anus. Episio-tomy, a deliberate oblique lateral surgical incision in the perineum, causes total rupture. The disadvantage of this procedure is that sexual intercourse is often painful after healing. Spontaneous rupture of the second degree almost always heals without causing problems, despite heavy internal and external stitching.