The fetus is born through the birth canal, which usually refers to the soft birth canal, including the cervix, vagina and perineum. The perineum is the last stage of the soft birth canal. The cervix and vagina need the exposed part of the fetus to expand slowly, and perineum expansion takes a while. It usually takes a long time for a fetus to be delivered from the birth canal, with an average of about two hours 1, and it will be longer for primiparas. The longer the time, the more chances the fetus will be deprived of oxygen. Therefore, lateral incision to enlarge perineum can protect the fetus and make it born as soon as possible. It has been proved that whether to do perineal lateral incision is directly related to whether the fetus is hypoxic and whether the newborn is asphyxiated.
When a pregnant woman gives birth, the mucosal folds inside the vagina are fully unfolded, and the muscle layer in the middle is fully expanded, so that the fetus can leave the uterus and come to the world through the vagina. Although the anatomical and physiological characteristics of the vagina are conducive to the smooth delivery of the fetus, in fact, when the fetal head with a diameter of 10 cm is delivered, there will be many perineal lacerations of different degrees without the help of a midwife. Once laceration occurs, postpartum will leave different degrees of sequelae. For example, some parturients suffer from serious vaginal and perineal injuries, resulting in uterine prolapse and even anal sphincter and rectum tearing, which leads to incontinence and is very painful. If the lateral perineal incision can be done in time, the above sequelae will not appear.
Maternal women usually use a small amount of anesthetic when doing lateral incision, so there is no pain. After the fetus is delivered, align the lateral incision. After taking out the stitches five days later, it will return to its original state. It can be seen that lateral perineal incision is a good method to prevent perineal tear and protect parturient. Clinically, there are some situations that require parturient to do perineal lateral incision:
① Poor elasticity of perineum, narrow vaginal opening or inflammation and edema of perineum. It is estimated that severe perineal tear will inevitably occur when the fetus is delivered.
(2) When the fetus is large, the position of fetal head is not correct, the productivity is not strong, and the fetal head is stuck in the perineum.
③ Older women over 35 years old, or complicated with high-risk pregnancy such as heart disease and pregnancy-induced hypertension syndrome.
④ The cervix is fully open and the fetal head is low, but the fetus has obvious hypoxia, abnormal changes in fetal heart rate, uneven heartbeat rhythm, turbid amniotic fluid or meconium.
⑤ When forceps assist.
⑥ The parturient had vaginal injury repair.