The due date is usually 280 days from the first day of the last menstrual period, and the 280th day is the due date. For women with irregular menstrual cycles, there is no way to project the due date based on the first day of the last menstrual period, but at this time, you can check the size of the gestational sac, the time of the appearance of the fetal heart and germ, and the parietal and rump diameter through ultrasound to project the week of pregnancy, so that you can project the due date, and the projection error is usually not more than 1 week. In addition, in the early stages of pregnancy, you can determine the pregnancy week by checking the blood HCG and progesterone values, and you can also determine the number of days of pregnancy based on the date of intercourse to project the expected delivery date. If the pregnant woman does not remember the date of intercourse, she can roughly estimate the week of pregnancy based on the time of pregnancy reaction and fetal movement, but the error is large. If the pregnancy is conceived through assisted reproductive technology, the expected date of delivery can be projected based on the date of the relevant operation. The expected date of delivery can be both early and late, and the pregnancy should be checked on time, and if everything is normal for the fetus, the pregnant woman can wait for delivery without worrying. If the expected date of delivery is more than 1 week and there are no effective contractions, you should go to the hospital for a timely checkup, combine with the doctor’s opinion to comprehensively assess the maternal status and, if necessary, assisted intervention to deliver the baby as soon as possible to avoid the impact on the fetus.