The expected date of delivery for regular menstruators is usually January 24 of the following year for the last menstrual period of 4.17. However, errors can occur for irregular menstruators, and can be estimated under the guidance of a doctor. For regular menstruators, pregnancy is counted from the first day of the last menstrual period and lasts about 280 days (40 weeks) in total. The due date is calculated from the first day of the last menstrual period, the month minus 3 or plus 9, and the number of days plus 7. Therefore, if the last menstrual period is April 17, the due date will be January 24 of the following year. For those who have irregular menstruation, the time of ovulation is variable, therefore, the pregnancy time cannot be estimated only according to the last menstruation, and it is necessary to combine with the ultrasound in early pregnancy to indicate the length of the head and hip to check the gestational week. Pregnant mothers should follow the doctor’s instructions to conduct reasonable and standardized obstetric examinations, so as to be able to timely detect and treat pregnancy complications, assess the safety of the pregnant woman and the fetus, and determine the timing and mode of delivery, so as to ensure the safety of mothers and infants.