The due date, as the name implies, is the expected date of delivery and the age of the fetus in utero is calculated in weeks. The maturity of the fetus can be determined based on the week of gestation. The period of 280 days (i.e. 40 weeks) after the first day of the last menstrual period is the period of fetal growth and development in the uterus. For example, for a mother whose last menstrual period is on December 20, the due date should be calculated as follows: 12-3=9 20+7=27. The due date is September 27 of the following year. Many people may ask the question: The first day of menstruation is not the date when conception begins. Indeed, conception must occur during ovulation. For women with regular menstrual cycles, ovulation occurs about 14 days before the next menstrual period, although it can be shifted forward or backward. For mothers-to-be with irregular menstrual cycles, it is difficult to estimate the ovulation date, so clinically, ovulation is counted from the day of the last menstrual period. For some careful mothers-to-be, the basal body temperature can be measured or the date of intercourse can be used to know the exact date of ovulation and conception. The due date is not an exact date of delivery, and scientists have calculated that only about 53 mothers give birth on the due date. Is it abnormal to be “early” or “late”? Clinically, a full-term fetus is defined as a baby born between 37 and 42 weeks of gestational age, and about 80-90% of mothers give birth during this period. Those who deliver at less than 37 weeks are preterm babies, accounting for 5-10%. The younger the gestational age, the weaker the ability of preterm babies to live, and the folklore of “seven alive and eight not alive” is not based on science. If you have symptoms of labor before 37 weeks of pregnancy, you should go to the hospital immediately to keep the baby in the womb for as long as possible. It is a different matter if a pregnant woman with pregnancy complications (e.g. high blood pressure, bleeding from the placenta) has to give birth prematurely. If the fetus is in the uterus for too long, such as after 42 weeks, it is called an overdue fetus, and the proverbial “ripe fetus” is also unscientific. The placenta, which maintains the supply of oxygen and nutrients to the fetus, is at its peak at around 38 weeks and gradually declines thereafter. In some cases, the placenta degenerates early, and the longer the period, the worse it is for the fetus. Many mothers-to-be perform emergency cesarean section before 42 weeks of gestation due to low amniotic fluid, and the child comes out as an “overripe child”, with dry skin like a little old man, little amniotic fluid and sticky, mung bean porridge-like, such a fetus may die in the womb if born a few days later. The expected date of birth can only be speculated for mothers with irregular menstrual cycles, and these mothers should remember the date of early pregnancy reaction at the beginning of pregnancy; the record sheet of the first hospital checkup may have the size of the uterus and the result of the urine pregnancy test; the result of the first ultrasound and the time of the first fetal movement can also help the doctor to speculate the expected date of birth. It seems that the due date can remind you of the time frame for the safe birth of the fetus, but do not look at the due date as a precise date. You should be ready to give birth at 37 weeks of pregnancy, but do not be overly anxious and listen to the nature.