Pregnancy is usually delivered after 280 days, i.e. 40 weeks, which is 9 months and 10 days by month, but the pregnancy period varies from one pregnant woman to another. Pregnant women usually give birth after 40 weeks. In calculating the due date, the calculation is based on the period of last menstruation pushed back 40 weeks, the first 3 months of pregnancy is early pregnancy, 3 months to 7 months is middle pregnancy, and 7 months to the time of delivery is late pregnancy. Some pregnant women have irregular periods or errors in the date of their last menstrual period, which can lead to errors in the calculation of the expected date of delivery. However, most pregnant women give birth at 37-42 weeks, and those who give birth before 37 weeks are considered premature, while those who give birth after 42 weeks are considered overdue. Therefore, pregnant women should be ready to give birth at 37-42 weeks and go to the obstetrics and gynecology department in time to wait for delivery when regular abdominal pain and redness occur. In addition, pregnant women should clarify the menstrual cycle and the time of the last menstrual period when calculating the expected date of delivery to avoid miscalculation of the expected date of delivery, and pregnant women who cannot be clarified can have ultrasound examination to calculate the week of pregnancy.