Any pregnancy that reaches or exceeds 42 weeks (>=294 days) is called a post-term pregnancy. It accounts for 5-10% of the number of births. The perinatal mortality rate is about 3-6 times that of full-term births. The survival of the fetus in the uterus of a post-term pregnancy mainly depends on the function of the placenta. 1. If the placenta functions normally and the fetus continues to grow, the fetus is overweight at birth or even macrosomia or dystocia is caused by skull calcification; 2. The placenta ages and becomes dysfunctional due to expiration, and the placenta has insufficient blood flow and oxygen supply. The fetus no longer continues to grow and develop and becomes a "little old man" (overmature baby syndrome). Due to lack of oxygen, the fetus excretes meconium and amniotic fluid, fetal skin, amniotic membrane and umbilical cord. The score at birth is low and the mortality rate is high. The fetus of a primipara with a post-term pregnancy is more dangerous than that of a multipara. Harm to the fetus and mother: fetal distress, reduced amniotic fluid volume, difficult delivery and injury.