1.If the menstruation is regular, with a cycle of 28 to 30 days, the expected date of delivery is the month plus 3 or minus 9, and the number of days plus 7. For example, if the last menstruation is May 1, the expected date of delivery is February 8; if the last menstruation is November 28, the expected date of delivery is September 5. 2. Irregular menstruation or unclear last menstruation Usually irregular menstruation, with a cycle of 1 to 3 months or even a quarter, or simply do not remember when the last menstruation is, should be projected according to the results of multiple ultrasounds during early pregnancy. The gestational sac can be seen at 5 weeks of pregnancy, the yolk sac can be seen at 6 weeks, the fetal heartbeat can be seen at 7 weeks of pregnancy, and the head-rump diameter is measured after 8 weeks, and the length of the head-rump diameter plus 6.5 equals the week of pregnancy. Based on the date of the examination and the size of the gestational week determined by ultrasound, the expected date of delivery can be calculated. The smaller the gestational week, the smaller the error, and the more accurate the projected due date. 3.Last menstruation is unknown, no early pregnancy ultrasound Last menstruation is unclear, and pregnancy is not discovered until there is fetal movement. You can recall when you started to have nausea and vomiting reaction (usually early pregnancy reaction starts to appear at 6 weeks of pregnancy) and when you started to have fetal movement (usually fetal movement starts to appear at 18-20 weeks), and then estimate the expected date of delivery roughly according to the ultrasound results. 4. Irregular menstruation, know the time of ovulation Nowadays, many people plan to get pregnant, they will test ovulation by ovulation test paper to know the specific time of ovulation. The date of ovulation is two weeks backward from the day of ovulation, recorded as the last menstruation, and then calculated according to the formula of menstrual rules. For example, if the day of ovulation is May 10th, the last menstrual period will be April 26th and the expected date of delivery will be February 3rd. 5, separated from each other Couples who are separated from each other, usually do not remember the last menstruation time, just after a family visit to get pregnant, the family visit day as is the day of ovulation, according to the fourth point of the method to calculate the last menstruation and the expected date of delivery. 6.Only know the date of intercourse The last menstruation is not clear, nor do you know the date of ovulation, nor is your menstruation regular, but you only know the date of intercourse, and the date of intercourse will be taken as the date of ovulation, and the expected date of delivery will be calculated according to the method of the fourth point. 7. IVF In the case of IVF, in many cases, menstruation is not allowed, and the time of transferring embryos is usually the 18th day of menstruation. If you count backwards 18 days from the day of transfer to the first day of the last menstrual period, then calculate the due date according to the formula.