Many women who are pregnant do not know how to calculate the pregnancy cycle, but in fact, it is very simple to calculate the pregnancy cycle, which in medical terms is calculated in weeks, 4 weeks (28 days) is one month, and the whole pregnancy cycle is 280 days, which is October. The week of pregnancy is calculated from the first day of the last menstrual period, not from the day of the clean period. For example, if your last period is on January 1, you will be 60 days pregnant on March 1, which is 8 weeks of pregnancy. Generally rough calculation, you can add one week out of three months, such as 3.2 last menstruation, 6.2 that is (3×4) + 1 = 13 weeks; the due date is the month plus 9 or minus 3, the date plus 7; such as 3.2 last menstruation, the due date is March + 9 = December, 2 + 7 = 9, that is, December 9. If it is April 2, the due date is 4-3=January, and the date is 9, which is January 9 of the next year. Some women who cannot remember the time of their last menstrual period can calculate the last menstrual period backwards by using the gestational age determined by ultrasound at the time of the earliest determination of pregnancy and visible fetal heartbeat. The fetal biparietal diameter, femoral length, head circumference and abdominal circumference measured by ultrasound can be used as a reference to estimate the number of weeks of pregnancy. The pregnancy cycle can be used to estimate the expected date of delivery. However, it is normal to have a full-term delivery within 21 days early or 14 days late, but if the delivery is not yet spontaneous 7 days after the due date, i.e. 41 weeks, you should be hospitalized to facilitate the delivery to avoid the risk of obstructed labor or intrauterine hypoxia due to prolonged delay. The different pregnancy cycles require different prenatal checkups, such as Down’s syndrome screening from 16 weeks to 18 weeks of pregnancy and ultrasound for systematic screening of malformations from 22 to 26 weeks of pregnancy, which can clearly understand the growth and development of the fetus in the womb.