The gestational week of pregnancy is usually estimated from the first day of the last menstrual period. There are various methods of estimating the gestational age, including the age of fertilization, the age of menstruation, the age of sexual intercourse, and the time of appearance of the ossification center and the development of the embryo can be used to estimate the time of pregnancy. For women with regular menstrual cycle, the gestational week is calculated from the first day of the last menstrual period, and the expected date of delivery is +9 or -3, date +7 of the month of menopause; for women with irregular menstrual cycle, the gestational week can be estimated more accurately by measuring the fetal head-rump length between 11-13 weeks +6 days of gestation, and the expected date of delivery can be corrected; if you miss the early pregnancy test, the mid-pregnancy period is 14-22 weeks by ultrasound measurement of biparietal diameter, head circumference and abdominal circumference, and The gestational age can be determined by ultrasound measurement of biparietal diameter, head circumference and abdominal circumference, and femur length. The gestation period is divided into early pregnancy, mid pregnancy and late pregnancy, and there are different physiological changes in different periods, so regular prenatal checkups should be conducted regularly, with the first checkup starting from early pregnancy.