The common methods of calculating the expected date of delivery are as follows.
1, the last menstruation calculation method: the month of the last menstruation minus 3 (insufficient plus 9) or the month directly plus 9 can also be, the number of days plus 7, that is, the expected date of delivery. For example, if the last menstrual period started on March 5, the expected date of delivery will be December 12 of the same year. (This method is simple and easy to understand, most people can use).
2. Calculation by the day of fertilization: If you know the day of fertilization, the expected date of delivery is 38 weeks (266 days) from this day. Those who use basal body temperature know the day of ovulation, then the day of fertilization can be calculated. This is more accurate than the method of calculating the due date from the day of the last menstrual period.
3. Estimation from the size of the uterus: The number of weeks of pregnancy is determined from the height of the uterine fundus (this is suitable for pregnant women who really do not know the date of their last menstruation or the date of fertilization). However, this method can only be determined by a professional obstetrician and gynecologist after specific measurements!
4.Ultrasound (ultrasound) method: This is a more accurate method for those who are not sure about the date of the last menstrual period. Since the size of the fetal sac and the length of the fetal head to the buttocks can be calculated, as well as the interparietal diameter on both sides of the fetal head, the number of weeks of pregnancy and the expected date of delivery can be deduced from this value. (However, from my experience as a doctor, the first ultrasound is the most accurate when the sac is detected in the uterine cavity, because once the fetus is big, it is not easy to judge, after all, some children are big and some are small!) (After all, some children are big and some are small!).
The most common method of calculating the due date is the date of the last menstrual period.
What to do after the due date
It is normal to give birth within two weeks before or after the due date. If the baby is born between 24 and 36 weeks of pregnancy, it is considered a premature birth (early birth), and if the birth is delayed from the expected date, i.e. after the 42nd week, it is a late birth (late birth). If a pregnant woman is past her due date and has not yet shown signs of labor, she must pay attention to the following points.
1.Continue with your maternity checkup and tell your doctor the results of your early pregnancy tests (such as ultrasound, blood tests, pregnancy tests, etc.) and the time and results of fetal movements, so that your doctor can check your pregnancy week again.
2, do not be too nervous, even if the pregnancy week is accurate, delivery within two weeks after the expected date of delivery will have little effect on mother and baby, but pay attention to the fetal movement. Once the fetal movement is less than 3 times per hour or less than 20 times in 12 hours or the fetal movement is weakened, you need to go to the hospital immediately for further examination, and the doctor will decide the timing of delivery according to the situation.
3.Strengthen prenatal checkups, shorten the interval between checkups, keep in touch with the doctor to inform the intrauterine fetal movement, and follow up the amniotic fluid volume with ultrasound. If there is no abnormality, the pregnancy can be continued under close supervision.
If the due date is postponed to 14 days later, when it reaches the clinical so-called overdue pregnancy, it is more dangerous for the child because the placenta of some pregnant women will be aging and the fetus will be suffocated by lack of oxygen, so timely measures should be taken at the hospital.
Other methods of calculating the expected date of birth
1. Calculation according to the date of fetal movement.
The fetal movement of first-time mothers appears in the 18th week of pregnancy, and menstruating mothers, because of their experience, can feel the fetal movement at the end of the 16th week, 2 weeks earlier than first-time mothers.
Therefore, the calculation formula is as follows
The expected date of delivery for primigravida = the date of fetal movement + 22 weeks.
The expected date of delivery for menstruating mothers = the date of fetal movement + 24 weeks.
In addition, if a pregnant woman cannot remember the time of her last menstruation and has no early pregnancy reaction, and has not yet felt the fetal movement, she can be assisted by her doctor to estimate the expected date of birth through ultrasound and the height of the uterine fundus.
2.Calculation according to the basal body temperature curve.
Take the last day of the low temperature section of the basal body temperature curve as the day of ovulation, and project backward from the day of ovulation to 264-268 days, or add 38 weeks.
3.According to ultrasound examination.
The gestational age can be estimated by measuring the inter-parietal diameter of the fetal head, the head-rump length and the femur length when the doctor does the ultrasound, and the expected delivery date can be projected (this method is mostly used as a diagnostic application for the doctor’s ultrasound examination).
4.Projected from the time of the beginning of pregnancy vomiting.
Reactive vomiting usually appears at the end of the 6th week of pregnancy, which is 42 days after the last menstrual period, from which it can be projected backward to 280 days, which is the expected date of delivery.
Therefore, the calculation formula is
The expected date of delivery = the date of early pregnancy reaction + 34 weeks.
5.According to the height of the fundus of the uterus
If you can’t remember the date of your last menstrual period, you can roughly estimate the expected date of delivery according to the height of the uterine fundus. At the end of April, the height of the uterus is between the navel and the upper edge of the pubic bone (10 cm above the pubic symphysis); at the end of May, the bottom of the uterus is two fingers below the umbilicus (16-17 cm above the pubic bone); at the end of June, the bottom of the uterus is flat on the navel (19-20 cm above the pubic bone); at the end of July, the bottom of the uterus is three fingers above the umbilicus (22-23 cm above the pubic bone); at the end of the eighth month of pregnancy, the raphe of the bottom of the uterus is in the middle of the umbilicus (24-20 cm above the pubic bone). At the end of the tenth month of gestation, the height of the uterine fundus returns to that of the eighth month, but the abdominal circumference is larger than that of the eighth month.
Retrograde menstruation method
This is the most common method of calculation. To reverse the calculation based on 280 days (40 weeks), add 9 (or subtract 3) to the month of the day of the last menstrual period and add 7 to the date to calculate it. For example, if the date of the last menstruation is January 15, then 1 plus 9 equals 10, 15 plus 7 equals 22, and the expected date of delivery is October 22. If the last menstrual period is September 25, then 9 minus 3 equals 6, 25 plus 7 equals 32, the expected date of delivery is June 32, but there are only 30 days in June, so
Therefore, it can be deduced that it should be July 2. This inverse algorithm is based on a 28-day menstrual cycle and must be modified according to the length of the individual menstrual cycle.
Pregnancy Calendar Algorithm
With the commercially available gestational calendar in the form of a circle or disc, the number of weeks of pregnancy and the expected date of delivery can be calculated against the date of the last menstrual period. There may be a difference of 2 or 3 days between this method and the reverse menstrual algorithm.
Is the due date accurate or not?
A due date is not an exact date of delivery. Scientists have estimated that only about 53% of women give birth on their due date.
The due date can remind you of the time frame for the safe birth of your baby, but don’t take the due date so precisely. If there are no signs of labor at 41 weeks of pregnancy, you should be hospitalized for observation or induction of labor if possible.
Method of calculating the expected date of delivery
The method of calculating the expected date of delivery is: add 9 or subtract 3 to the number of the last menstrual month, and add 7 to the day. If you use the lunar calendar, the calculation method for the month is the same, but add 15 to the day. Example: The last menstrual period was on February 1, 1985
Date 1 + 7
Month 2 + 9
The expected date of delivery is: —– November 8 (85 years)
Last menstrual period is April 15, 1985
Date 15 + 7
Month 4 – 3
Due date is: —–1 22nd of November (’86)
If you can’t remember the date of your last menstrual period, you can roughly estimate the due date by the height of the uterine fundus. At the end of April gestation, the height of the uterus is in the middle of the navel and the upper border of the pubic bone (10 cm above the pubic symphysis); at the end of May gestation, the base of the uterus is 2 transverse fingers below the umbilicus (16-17 cm above the pubic bone); at the end of June gestation, the base of the uterus is flat on the navel (19-20 cm above the pubic bone); at the end of July gestation, the base of the uterus is three transverse fingers above the umbilicus (22-23 cm above the pubic bone); at the end of the eighth month of gestation, the raphe of the base of the uterus and the umbilicus are At the end of the tenth month of pregnancy, the height of the uterine fundus returns to that of the eighth month, but the abdominal circumference is larger than that of the eighth month.
The expected date of birth does not mean that the date is certain to be born, but only an approximate time, the birth of two weeks before and after the expected date of birth are within the normal range.