It is not always necessary to have a lateral incision to give birth to a baby. Whether or not a lateral incision is needed depends on the condition of the mother and the fetus at the time of delivery. If the condition of the birth canal is suitable for the fetus to be delivered smoothly, a lateral incision is usually not needed. If the woman has experienced labor, the birth canal is relatively loose, the fetus can be delivered smoothly, then there is no need for lateral incision. Second, the need for lateral incision 1, primigravida perineum is too tight or the fetus is too large: in this case, the fetus can not pass through the birth canal, at this time forced delivery may cause perineal laceration, usually need to carry out perineal circumcision, so as not to cause local lacerations, causing blood vessel rupture, or even hemorrhage; 2, maternal pathological conditions: the urgent need to end the pregnancy, need to carry out perineal circumcision. For example, if the mother has heart disease, high blood pressure or diabetes, the second stage of labor should be finished as soon as possible to let the fetus be delivered, so as to avoid over-fatigue of the mother, which may induce more serious conditions; 3, abnormalities of the fetus: if the fetus has any problems in the process of labor, such as contamination of amniotic fluid and deceleration of fetal heart rate, in order to avoid severe oxygen deprivation of the fetus, it is necessary to carry out a perineal lateral incision to speed up the process of labor. Therefore, there are indications for perineal circumcision, and doctors and midwives will choose whether or not to perform perineal circumcision according to the mother’s condition.