There are several methods to calculate the week of pregnancy: First, the week of pregnancy is calculated according to the last menstrual period, which is applicable to pregnant women with regular menstruation and a cycle of 28-30 days, counting from the first day of the last menstrual period, and dividing the total number of days by 7 is the number of weeks of pregnancy. Secondly, according to the time of early pregnancy reaction and fetal movement, it is applicable to pregnant women who have irregular menstruation or cannot remember the date of their last menstruation, as well as those who are pregnant after miscarriage or after delivery without menstruation. It is possible to roughly estimate the week of pregnancy according to the time of early pregnancy reaction or fetal movement. Early pregnancy reaction, such as nausea, vomiting, salivation and drowsiness, appears around 6 weeks after menopause. In the week of 18-20 weeks of menopause, the fetal movement can be felt 2 weeks earlier in menstruating women because they are more experienced and sensitive, and in the week of 16-18 weeks. Third, according to the size of the gestational sac, the size of the fetal parietal-rump diameter and the size of the biparietal diameter shown by ultrasound, the earlier the gestational week is projected, the more accurate it is.