There are several ways to calculate the pregnancy cycle and the pregnancy week after pregnancy: a. Calculation by menstruation, this is the most common method, if the woman usually has regular menstruation, the pregnancy week is calculated from the first day of the last menstruation, that is, from the first day of the menstruation in the month of sexual intercourse. From this time, the month plus 9 or minus 3, the time plus 7 days, the final time is the expected date of delivery, the normal pregnancy cycle is 280 days, that is, 40 weeks. Second, the calculation through ultrasound, mainly applies to the menstrual cycle is not allowed or did not record their own menstrual cycle, can be calculated through ultrasound, but the most accurate is the early pregnancy ultrasound and small four-dimensional ultrasound.