After pregnancy almost everyone knows that it is harmful to let the child be born early before the due date and that the child may not mature. But how long should the child stay in the mother’s womb? It is said that “one day in the mother’s womb is better than three days outside”. Therefore, some pregnant women are reluctant to be hospitalized and induced even after their due date has passed. From the physiological point of view of pregnancy, the whole period of pregnancy is 280 days on average from the day of the last menstrual period, and doctors often calculate it in terms of gestational weeks, that is, 40 gestational weeks. Preterm birth is called preterm birth when the baby is born between 28 weeks and less than 37 full weeks (196-258 days), when the baby has some immature organs and many complications; full-term birth is called full-term birth when the baby is born between 37 weeks and less than 42 full weeks (259-293 days), with statistics that 5% of the births are on the due date, 29% are around 3 days on the due date, and 80% are 2 weeks before and after the due date. In other words, most of the children are born in this period; pregnancy over 42 weeks (294 days and above) without delivery is overdue pregnancy, and the delivery in this period is called overdue delivery. The main risk of overdue pregnancy is the increase in perinatal morbidity and mortality, which increases with the length of gestation. There are several possible factors that can cause delayed birth of the fetus due to the unclear causes of human pregnancy and delivery. On the fetal side there is low fetal adrenocorticotropic hormone, or abnormal fetal position and oversized fetus, which predisposes to the inability of the fetal previa to directly compress the cervix and cause reflex uterine contractions, delaying the start of the labor process. Delayed pregnancy or even overdue pregnancy is not beneficial to the fetus, and will have some adverse reactions: the placenta can appear aging phenomenon is the most common, the placenta is the connection between the fetus and the mother, is the mother to provide nutrients and oxygen for the fetus, as well as the elimination of fetal metabolic products of the organ, the placenta aging will cause the fetus nutrient exchange and transfer capacity decreased, blood perfusion is insufficient, and lead to fetal ischemia, oxygen supply Inadequate oxygen supply. In mild aging, without stress, the fetus can compensate and no clinical manifestation can occur, but after delivery, the fetus cannot adapt to the uterine contraction and may soon become hypoxic and prone to accidents, including abnormal fetal heart rate, amniotic fluid and fetal fecal contamination, decreased fetal blood pH and fetal asphyxia after delivery; in severe placental aging, the fetus may have clinical symptoms of hypoxia before delivery and even fetal death in utero. The placenta may have clinical symptoms of hypoxia and even fetal death before delivery. Low amniotic fluid is a sign of low placental function and a reflection of chronic intrauterine hypoxia of the fetus. The amount of amniotic fluid starts to decrease after 38 weeks of gestation, and the amount of amniotic fluid at full term is about 1000 ml, with the delay of pregnancy, the amount of amniotic fluid becomes less and less, and at the end of pregnancy, the amount of amniotic fluid decreases significantly, so that the fetus is directly compressed by the contraction of the uterus and the umbilical cord is easily compressed. The amount of amniotic fluid doctors now often find out by B-type ultrasound examination or manual rupture of membranes. Due to prolonged pregnancy, the fetal skull hardens, the distance between the bones narrows, the plasticity of the fetal head decreases, labor is prolonged, the chance of cephalopelvic disproportion increases, and fetal distress increases, which increases the incidence of surgical delivery and birth injuries. The fetus has excessive maturity, the fetal fat disappears, the subcutaneous fat decreases, the skin is dry, loose and wrinkled, the hair is dense, the finger (toe) nail grows, the body is long and thin. The fetus looks like a “little old man”. And can also suffer from meconium aspiration syndrome and respiratory distress syndrome, the risk to the newborn is greater. Once a pregnant woman’s due date has passed, several issues should be noted: 1. whether the due date has really passed; 2. if the due date has indeed passed, but the placenta is functioning normally, the fetus continues to grow, so there is no danger; 3. if the pregnancy has expired, the placenta is not functioning, the fetus is at high risk. The calculation of the due date is based on the last menstruation of the pregnant woman, some pregnant women have irregular menstruation and the doctor will rely on other clinical examinations to project: the variability of menstruation; the basal body temperature before pregnancy; the date of early pregnancy reaction and the appearance of fetal movement; the size of the uterus during the gynecological examination in early pregnancy; the indicators of the fetus measured by B-ultrasound before 20 gestational weeks and various other factors are combined to estimate. Therefore, pregnant women should start regular prenatal checkups before 12 gestational weeks to allow the doctor to have a series of observations and to be able to estimate the expected date of delivery more correctly to avoid unnecessary induction of labor. When the due date has indeed passed, it is necessary to check the placental function, which can be determined by self-monitoring of maternal fetal movements, daily fetal movement count; detection of maternal urine E3; monitoring of fetal heart rate; biophysical detection by ultrasound, etc. If the test is normal, labor can be induced when the pregnancy is close to term. If the placenta is not functioning well or the fetus is at risk a direct cesarean section can be performed. Timely and appropriate management can save the life of the newborn and reduce complications.