What are the methods for calculating gestational age?

After becoming pregnant, many women will calculate their due date to know when the baby will be born. Of course, the gestational age is not absolute. It is only calculated based on the patient's pregnancy time and can only be used as a reference. There are many ways to calculate the gestational period, such as starting from morning sickness, calculating based on B-ultrasound, etc. The gestational period also varies with different calculation methods. So what are the methods for calculating the gestational period?

The main calculation methods are as follows:

Method 1 for calculating gestational period: 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 July 17, 2008, and the expected date of delivery is approximately April 24, 2009. You can also calculate backwards from the first day of the last menstrual period to the 280th day, which is the expected date of delivery.

Method 2 for calculating pregnancy period: Calculate based on fetal movement date

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.

Method 3 for calculating pregnancy and delivery period: Calculation based on 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.

Method 4 for calculating the gestational period: 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. Counting backward from this to 280 days is the pregnancy period.

Method 5 for calculating gestational period: 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).

Method 6 for calculating pregnancy and delivery period: 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.

Method 7 for calculating pregnancy and delivery period: 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 the fourth month of pregnancy, 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 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.

The above are the main methods for calculating gestational age. Calculating the gestational age is a concern for most pregnant women, and many pregnant women will also consult their doctors about their gestational age during prenatal check-ups in the hospital. Patients should have a correct understanding of the pregnancy and delivery period and not be afraid of the symptoms that appear in the body as the pregnancy and delivery period approaches. The fetus will mature after a certain month of pregnancy, and the pregnant woman's body will show many pre-delivery symptoms. When delivery symptoms appear, she must go to the hospital for examination and wait for delivery.