A woman’s pregnancy is counted as 1 gestational month of 28 days from the first day of her last menstrual period, and 280 days, or 10 months, of pregnancy. Medically, 4 weeks is usually considered as 1 month, and 10 months or 40 weeks of pregnancy is the expected date of delivery, which can usually be 1 week on or around the expected date of delivery. Irregular menstruation may cause the due date to be inaccurate, so early pregnancy tests can be based on the time of positive urine HCG, the value of blood HCG, and the size of the fetus at the earliest ultrasound to estimate the week of pregnancy. For example, if the size of the fetal bud in early pregnancy is 1 week smaller than the actual gestational week based on the last menstrual period, the expected date of delivery should be pushed back by 1 week. Generally, children born between 37 and 42 weeks of gestation are called full-term pregnancies, where all organs and systems of the fetus are well developed and ready to be born; children born before 28 weeks of gestation are premature, and because the gestation is less than 37 weeks, the fetal organs are not yet well developed, the fetal lungs are immature, and emergencies such as respiratory distress syndrome are likely to occur, and the smaller the gestational week, the lower the fetal survival rate. The smaller the gestation period, the lower the survival rate of the fetus. Those who have reached or exceeded 42 weeks of gestation and have not yet given birth are considered to have an overdue pregnancy, when the function of the placenta is gradually declining and the fetus may have insufficient oxygen, nutrition or blood supply in the uterus, which may lead to intrauterine distress.