The number of weeks of pregnancy is calculated from the first day of the last menstrual period until the time of the examination, and the number of weeks elapsed is the number of weeks of pregnancy. The expected date of delivery is also calculated from the first day of the last menstrual period, the month minus three, and the number of days plus seven, and it is generally normal to deliver two weeks before or after the expected date of delivery. If you do not remember your last menstrual period, or if you are breastfeeding and do not have a period, you should go to the hospital to have an ultrasound test to estimate the number of weeks of pregnancy and the expected date of delivery. Correctly projecting the number of weeks of pregnancy and the expected date of labor can effectively help pregnant women determine the examination of each time period, so as to make sufficient preparations for the delivery period, and also effectively ensure the safety of the fetus and pregnant women.