Late ovulation usually requires verification of the gestational week by ultrasound examination in early pregnancy, and the number of weeks of pregnancy as well as the expected date of delivery are projected based on the size of the gestational sac, the size of the fetal buds, or the diameter of the head and buttocks, but there are some errors. For women with late ovulation, calculating the week of pregnancy according to the first day of the last menstrual period does not correspond to the actual size of the developing embryo. Therefore, for women with late ovulation, to determine whether the embryo is developing normally, you need to compare the size of the embryo with the size of the embryo at the time of the first ultrasound. For women with normal menstrual cycles, the number of weeks of pregnancy should be calculated from the first day of the last menstrual period. During pregnancy, it is recommended to undergo regular checkups to determine the development of the fetus based on the results of the checkups.