The last menstrual period was on April 22nd and the due date is January 29th of the following year. The gestation period is calculated from the first day of the last menstrual period and is approximately 280 days (40 weeks). In clinical practice, for women with regular menstrual periods, the expected date of labor is calculated as the month of the last menstrual period plus 9 or minus 3, and the date plus 7. Generally speaking, if the last menstrual period is in March or before, then the month plus 9 and the date plus 7 will be the expected date of labor; if the last menstrual period is in April or after, then the month minus 3 and the date plus 7 will be the expected date of labor; if the date plus 7 is greater than the maximum number of days in the month, then it will be postponed to the next month. Therefore, if the last menstrual period is April 22nd, the expected date of delivery is January 29th of the following year. If the pregnant woman’s menstruation is irregular before pregnancy, she can go to the regular hospital in early pregnancy to check the ultrasound to determine the size of the fetus and the week of pregnancy, in order to determine the expected date of delivery.