Conception occurs in the fourth month of the lunar calendar and delivery takes place in January or February of the following year. The clinical due date is based on the date of the first day of the mother’s last menstrual period. If the month is less than 3, the expected month of labor is added to 9 and the date is added to 7. If the month is greater than 3, the expected month of labor is subtracted from 3, and the date is added to 7. For the lunar calendar, the month is the same, and the date is added to 15, or the lunar time is converted to solar time and then projected. If the time of conception is based on coitus, then add 14 to the above algorithm. Thus, a woman who conceives in the fourth month of the lunar calendar will give birth in January or February of the following year. However, due to the differences or irregularities in women’s menstrual cycles, the expected date of delivery can be calculated by correcting the week of pregnancy based on the estimation of biparietal diameter or femur length on the basis of obstetric ultrasound.