Will the due date be correct if the menstruation is irregular?

For many expectant mothers, it is necessary to calculate the due date. Only by making preparations before the due date can you reduce some of the threats. But some mothers are worried that if their menstruation is irregular, will their due date be incorrect as well? Generally speaking, there is not much relationship between menstruation and due date. The due date can only be an estimate of the delivery date and is not completely accurate.

Since it is difficult for every pregnant woman to accurately determine the time of conception, medical regulations stipulate that the expected date of delivery is calculated from the first day of the last menstrual period. The entire pregnancy period is 280 days, or 10 gestation months (each gestation month is 28 days).

The due date can remind you of the time range for the safe birth of the fetus, but don't take the due date too precisely. By the 37th week of pregnancy, you should be prepared for delivery at any time, but don't be too anxious, just let nature take its course. If there are no signs of delivery by the 41st week of pregnancy, you should be hospitalized for observation or induced labor if conditions permit. [2]

(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 on February 1, 1985, month 2+9, day 1+7, expected date of delivery = November 8 (1985)

The last menstrual period was April 15, 1985, month 4-3, date 15+7, due date = January 22 (1986)

(2) Calculated based on the date of fetal movement:

If you can't remember the date of your last menstrual period, you can calculate it based on the date of fetal movement. Fetal movements usually begin between 18 and 20 weeks of 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) Calculated based on 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 264-268 days, or 38 weeks.

(4) Calculation based on B-ultrasound examination:

Doctors can estimate the gestational age by measuring the biparietal diameter, crown-rump length, and femur length during B-ultrasound.

And calculate the expected date of delivery (this method is mostly used by doctors for B-ultrasound diagnosis).

(5) Calculate from the time when morning sickness starts:

Morning sickness usually occurs at the 6th week of pregnancy, which is 42 days after the last menstrual period. The expected date of delivery is 280 days after the last menstrual period.

(6) Roughly estimate based on the height of the uterine fundus

If you can't remember the date of your last menstrual period, you can roughly estimate the expected date of delivery based on 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 of pregnancy, the uterine fundus is 2 horizontal fingers below the navel (16-17 cm above the pubic bone);

At the end of the sixth month of pregnancy, the uterine fundus is level with the navel (19-20 cm above the pubic bone);

At the end of the seventh month of pregnancy, the uterine fundus 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 uterine fundus is located midway between the umbilicus and the navel (24-25 cm above the pubic region);

At the end of the ninth month of pregnancy, the uterine fundus 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 uterine fundus returns to the height at eight months, but the abdominal circumference is larger than at eight months.