1、会阴及阴道裂伤：正常情况下，会阴及阴道的伸展性很大，临产后胎头下降，提肛肌向两侧扩张，会阴体也随之变博，有利于胎头娩出，当胎头与产道不相适应时，例如胎儿过大；产道狭窄；过期妊娠；胎头较硬不易变形，会阴坚韧或有疤痕不易扩张时；产刀过强、息产、或产道扩张不 1, perineum and vaginal laceration: Under normal circumstances, the perineum and vaginal extension of a large, fetal head after childbirth drop, mention levator ani to both sides of the expansion, the perineal body also will be Bo, is conducive to fetal head was delivered, when Fetal head and birth canal do not match, for example, the fetus is too large; birth canal is narrow; outdated pregnancy; fetal head hard and not easy to deformation, perineal tough or difficult to expand when the scar;