How to calculate the due date most accurately

When many pregnant women are undergoing prenatal checkups, doctors will actually make a preliminary estimate of the expected delivery date so that the pregnant women and their families can make adequate preparations. Generally, the due date is calculated from the first day of the last menstrual period, and the due date is 280 days later. The expected date of delivery is not completely accurate because it varies from person to person, so pregnant mothers should do relevant prenatal examinations.

How to calculate the due date? The due date is the date when the pregnant woman is expected to give birth. Since it is difficult to accurately determine the time of conception in a pregnant woman, medical regulations stipulate that the expected date of delivery is calculated from the first day of the last menstrual period, and the pregnancy lasts about 280 days, which is 40 weeks, equivalent to 10 months. The expected date of delivery can generally be calculated using the following methods:

1. Calculated based on the last menstrual period :

Add 9 or subtract 3 from the month of the last menstrual period to get the month of the expected delivery date; add 7 to the day of the last menstrual period to get the day of the expected delivery date.

For example: the last menstrual period was April 15, 2014, date 15+7=22, month 4-3=1, and the expected date of delivery is January 22, 2015.

2. Calculate based on fetal movement date :

If a pregnant woman cannot remember the date of her last menstrual period, she can calculate it based on the date of fetal movement. Generally, fetal movement begins 18-20 weeks after pregnancy. The calculation method is: for primiparas, it is the day of fetal movement plus 20 weeks; for multiparas, it is the day of fetal movement plus 22 weeks.

3. Calculate according to the basal body temperature curve :

The last day of the low temperature segment of the basal body temperature curve is regarded as the ovulation day, and the ovulation day is counted back to 264-268 days, or 38 weeks.

4. Calculation based on B-ultrasound examination :

When the doctor performs an ultrasound, he or she can estimate the gestational age and calculate the expected date of delivery based on the measured biparietal diameter, crown-rump length, and femur length.

5. Calculate from the time when morning sickness starts :

Morning sickness usually occurs at the sixth week of pregnancy, which is 42 days after the last menstrual period, and the expected date of delivery is 280 days.

6. Roughly estimate based on the height of the uterine fundus :

If the date of the last menstrual period is unclear, pregnant women can also roughly estimate the due date based on the height of the uterine fundus. At the end of the fourth month of pregnancy, the height of the pregnant woman's uterus is between the navel and the upper edge of the pubic bone (10 cm above the pubic symphysis); at the end of the fifth month of pregnancy, the fundus of the uterus is 2 horizontal fingers below the navel (16-17 cm above the pubic bone); at the end of the sixth month of pregnancy, the fundus of the uterus is level with the navel (19-20 cm above the pubic bone); at the end of the seventh month of pregnancy, the fundus of the uterus is three horizontal fingers above the navel (22-23 cm above the pubic bone); at the end of the eighth month of pregnancy, the xiphoid process of the fundus of the uterus is in the middle of the navel (24-25 cm above the pubic bone); at the end of the ninth month of pregnancy, the fundus of the uterus is 2 horizontal fingers below the xiphoid process (28-30 cm above the pubic bone); at the end of the tenth month of pregnancy, the height of the fundus of the uterus returns to the height at the eighth month, but the abdominal circumference is larger than that at the eighth month.

Most pregnant women will make corresponding arrangements based on their due date, but in fact the due date is only an approximate time, not the exact date of delivery. The time of fetal delivery is affected by many factors, and for women with irregular menstrual cycles, the time of ovulation and conception is difficult to determine. Only about half of pregnant women will give birth on the due date.