The number of days of pregnancy can be calculated from the size of the gestational sac and also from the last menstrual period. The size of the gestational sac increases with the number of days of pregnancy, so it is possible to calculate the number of days of pregnancy from the size of the sac during early pregnancy, and the earlier the week of pregnancy, the more accurate it is. If you want to know the number of days of pregnancy, for women with regular menstrual cycles, you can also calculate the number of days according to the time of your last menstrual period, taking the first day of your last menstrual period as the starting point, and the number of days between them as the number of days of pregnancy. If you are not sure how to calculate the number of days, you can also consult your obstetrician. For women in early pregnancy, it is more accurate to judge the number of days of pregnancy based on the size of the gestational sac. Regular pregnancy checkups are needed during pregnancy to observe the development of the fetus. If you find that the embryo development is delayed, or the fetus stops developing, you need to further check and choose the appropriate treatment.