Pregnancy by intercourse on the tenth day of menstruation will not be on the large side of the gestational week. Usually the estimated due date is calculated from the first day of the last menstrual period, the month minus 3 or plus 7, and the number of days plus 7, independent of the day of intercourse. After pregnancy, ultrasound is needed to re-verify the due date. Early ultrasound monitoring of fetal head and hip length is an accurate way of estimating the gestational week, and when the difference between the early pregnancy ultrasound projection and the menstrual projection of the gestational week is greater than 5 days, then the pregnancy ultrasound is used to correct the due date. Therefore, the week of pregnancy is calculated on the first day of the last menstrual period in conjunction with the head and hip length of the early pregnancy ultrasound, and has nothing to do with the tenth day of menstruation coitus pregnancy. Therefore, when you find out that you are pregnant, you need to go to the hospital to have an ultrasound examination in time to calculate the week of pregnancy more accurately.