Estimation of expected date of confinement (EDC) is a key concern after determining pregnancy. Most of our pregnant friends, who have more or less some knowledge about the expected date of confinement, still do not know enough and have many misconceptions, so it is necessary to elaborate on them here. It is crucial to clarify the last menstrual period (LMP). In clinical experience, the exact date of fertilization (or date of intercourse) for women is often not easy to clarify, while the last menstrual period is remembered more deeply by most pregnant women. The average human gestation period is about 280 days (40 weeks of menopause) from the first day of the last menstrual period, and ovulation is often in the middle of the menstrual cycle, so the actual duration of pregnancy (from fertilization to delivery) is about 266 days on average. It is customary to calculate the expected date of delivery by subtracting 3 from the month of the last menstrual period and adding 9 if it is not enough, and adding 7 to the number of days (Naegele’s rule). If the last menstrual period was on August 8, 2008, the expected date of delivery would be May 15, 2009. In the case of pregnant women whose entire pregnancy does not include the month of February, their due date will be calculated as above and then subtracted by 2 days. Some rural pregnant women in the clinic only remember the lunar calendar, then the number of days according to the lunar calendar should be added 14, of course, it is best to convert to the Gregorian calendar and then project. These methods are based on the premise of the 28-day menstrual cycle, women from ovulation to the next menstrual period, that is, the luteal phase is generally more fixed 14 days, so the length of the menstrual cycle also affects the date of delivery, the expected date of delivery will need to be corrected. If a pregnant woman has a normal cycle of 28 plus or minus X days, the date calculated by the above method should also be plus or minus X days. In addition, there is a gestational disc calendar algorithm: there will be 2-3 days error; basal body temperature curve method: generally 24 hours before and after ovulation is considered the day of fertilization, ovulation day: month plus 9, day minus 7, this method is very accurate. There are also special software for pregnancy week calculation on the Internet. There are always some pregnant women who have irregular menstrual cycles, cannot remember their last menstrual period, have memory deviations, or have not resumed menstruation after giving birth and breastfeeding. The actual gestational age can be estimated by the biparietal diameter (BPD) and femur length (FL). You can follow the chart, but be aware of the dynamic observation. It is important to note that the due date is not the day of delivery and that 280 days is a statistical average. The exact date of delivery is regulated by genetics, environment, nutrition, illness, emotions, sex, position and size of the fetus and many other factors. Mothers-to-be who are approaching their due date do not have to worry too much, less than 5% give birth exactly on their due date, but most pregnant women end their pregnancy within 38-41 weeks. The baby comes into the world. Method of assessing gestational age in early pregnancy: Gestational age (days) = average internal diameter of gestational sac (mm) + 30 Gestational age (weeks) = maximum diameter of gestational sac (cm) + 3 Gestational age (weeks) = CRL (cm) + 6.5 Gestational age (weeks) = (average internal diameter cm + 2.534) / 0.7 1- May months: length (cm) = number of months 2 , weight (g) = number of months 3 x 2; 6- Oct months. Length (cm) = number of months × 5, weight (g) = number of months 3 × 3. Fetal weight (g) = 900 × BPD (biparietal diameter) – 5200