A total of 40 weeks of pregnancy, i.e., 10 months of pregnancy, with 4 weeks as a unit of gestational age. Counting from the first day of the last menstrual period, the whole pregnancy lasts an average of 280 days. What is usually called the menstrual age, from the first day of the last menstrual period to fertilization takes about 14 days, so the menstrual age is 2 weeks longer than the actual embryo development time. Calculation of the expected date of delivery is as follows: using the Negler’s Rule, the worldwide common method of calculating the expected date of delivery, which is extrapolated from the 1st day of the last menstrual period by adding 7 days to the number of days and subtracting 3 or adding 9 to the number of months. pregnant women using the lunar calendar are required to convert the 1st day of the last menstrual period into the Gregorian calendar in order to calculate the expected date of delivery. If the last menstrual period is uncertain, unreliable or abnormal, an early ultrasound can be used to determine the expected date of labor. Calculation of the expected date of labor and the week of pregnancy should never be neglected, as miscalculation can lead to serious errors in diagnosis and treatment. Once the expected date of labor has been determined, it should not be changed easily, and reasons for the change should be documented if a change is needed.