The calculation of the pregnancy cycle is mainly as follows: 1. In case of pregnant women with regular menstrual cycles in the past, the last menstrual period shall prevail, that is, the first day of the last menstrual period, for example, February 1, 2019 is the date of the last menstrual period, the expected date of delivery is the month plus 9 and the day plus 7, then the expected date of delivery is November 8, 2019; 2. In case of patients with irregular menstrual cycles, especially NT is usually performed during 11-13 weeks, if menopause is more than three months, ultrasound indicates only six weeks plus, and menopause is more than five months, ultrasound indicates only 11 weeks, we should make a comprehensive assessment. If you have been pregnant for three months and the ultrasound indicates only six weeks plus, or if the ultrasound indicates only 11 weeks after five months of menopause, a comprehensive assessment should be made to estimate the expected date of delivery.