1. Calculation method of days of pregnancy During pregnancy, the calculation of days of pregnancy is very important because it can help doctors judge the growth and development of the fetus and determine the expected date of delivery. Usually, the number of days of pregnancy is calculated from the first day of the last menstrual period to the expected date of delivery. This means that, without artificial insemination, a woman with normal conception would be pregnant for about 280 days or 40 weeks. 2. Early pregnancy