How to calculate fetal weeks

According to folk tradition, it is said that a woman usually needs to carry the baby for ten months. In fact, according to current scientific calculations, pregnancy is usually not ten months. Most pregnant women are asked about their last menstrual period during prenatal checkups. Doctors usually calculate the expected date of delivery based on the last menstrual period and then ask pregnant women to prepare for delivery. However, most people do not have a particularly good understanding of how to calculate the number of fetal weeks.

How to calculate fetal weeks?

1. Calculated based on the last menstrual period

If a pregnant woman has a regular menstrual cycle, she will have her period every 28-30 days and her last period is remembered accurately. It can be calculated by the formula. The formula is based on the fact that the gestation period is 280 days in total, which can be calculated as one month every 30 days, for a total of 9 months and 10 days. Some months are long and some are short. If it is February, there are only 28 or 29 days. Generally speaking, if we calculate it as three long months, it will be 9 months and 7 days. Therefore, the formula is as follows: The expected date of delivery is equal to the month of the last menstrual period minus 3, and then the number of days plus 7. If the pregnant woman's menstrual cycle is short, with menstruation occurring every 25-26 days, 2 days can be subtracted from the previous date. If the cycle is long, with menstruation occurring every 35 days, 7 days can be added to the previous date. The same can be said for other situations.

2. Calculate according to the date of early pregnancy reaction

Some women have irregular menstrual cycles, or have forgotten the date of their last menstrual period, or have become pregnant again after giving birth or having a miscarriage but have not had their period yet. As long as they remember the time when early pregnancy symptoms such as nausea and vomiting occurred, they can also use the industry to calculate the expected date of delivery. Since early pregnancy symptoms usually occur around 6 weeks of gestation, the calculation formula is: expected date of delivery = date of onset of early pregnancy symptoms plus 34 weeks.

3. Calculate by the date of fetal movement

The fetal movement of a primipara occurs around the 18th week of pregnancy. Because multiparas have experience, fetal movement occurs 2 weeks earlier than primiparas. Therefore, the calculation formula is: The expected date of delivery for primiparas = the date of fetal movement + 22 weeks. The due date for multiparous women is the date of fetal movement plus 24 weeks.

4. Calculation based on B-ultrasound examination:

When doctors perform B-ultrasound, they can measure the biparietal diameter of the fetal head, the crown-rump length and the femur length to estimate the gestational age 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.