Gestational age is calculated from when?

The article was professionally consulted by BSCK II Pham Thi Tuyet Mai - Department of Obstetrics and Gynecology - Vinmec Hai Phong International General Hospital.

Gestational age is one of the important factors in assessing fetal development. The methods of calculating gestational age may deviate slightly from reality but will not be too large. Knowing the exact gestational age can help you proactively take care of yourself and your baby. Therefore, you should go to the doctor and monitor your pregnancy periodically during pregnancy.

Fetal age is usually calculated by the number of weeks of pregnancy.
The normal course of pregnancy is divided into 3 stages as follows:
First 3 months: Week 1 - 13th week (starting from fertilization - 3rd month) Second 3rd trimester: 14th week - Week 2 27 (month 3 - 6 months) Last 3 months: Week 28 - 42 weeks (month 6 - month 9) Knowing the exact gestational age is very important in pregnancy, because in addition to helping Mothers check the development of the fetus, this is also an important factor for pregnant women to prepare for the time of their birth.
Besides, thanks to the gestational age, the doctor can know the details of the baby's growth and body development and help the doctor make a safer and more accurate antenatal checkup.

When you find out you are pregnant, many women will not be able to know what week they are pregnant, so they will find out how gestational age is calculated.
Currently there are many ways to calculate the age of the fetus, but to calculate the exact week of the fetus is not simple. Here are a few ways to help you calculate your baby's age.
2.1. How to calculate gestational age based on menstrual date So when applying the method to calculate gestational age based on menstrual day, from what day do you start to calculate gestational age? Accordingly, the doctor will calculate the gestational age based on the last menstrual period. Specifically, the first day of the last menstrual period is counted as the first day of pregnancy. This is a simple method of calculating gestational age, which does not require high qualifications or equipment.
Under this method, gestational age will be calculated starting before the actual date. But because no one can know the exact date of ovulation, the time of conception, but the menstrual cycle knows exactly, so the doctor will ask the first day of the last period.
However, this method applies to women who have a regular 28-day menstrual cycle, remember the exact date of the start of the menstrual period. Not applicable to irregular menstrual cycle, do not remember the specific menstrual cycle.

2.2. Calculating gestational age by ovulation date Calculating gestational age by ovulation is quite accurate if a woman can accurately remember the date of sexual intercourse with the ability to conceive. Because the egg can only stay in the uterus for about 24 hours, the sperm can only fuse with the egg to form an embryo during this time.
This method is only applicable in cases where women have regular menstrual cycles and remember the exact date of ovulation and sex.
2.3. Ultrasound in the first 3 months of pregnancy During the first 3 months of pregnancy, the fetal development is less dependent on factors other than gestational age, so ultrasound assessment of gestational age will give the highest accuracy.
To determine gestational age, the doctor will measure the size of the gestational sac or the length of the baby's head - buttocks, from which it will calculate the gestational age according to the development of the fetus. This method can be applied in cases where the pregnant mother does not remember the first day of her last menstrual period or has irregular periods.
Although it has high accuracy, this ultrasound method requires professional qualifications of doctors as well as equipment to meet certain conditions.

2.4. Measuring the height of the uterus However, in cases where we do not remember the first day of the last menstrual period as well as have no conditions for ultrasound examination, we can estimate the gestational age by measuring the height of the uterus (the distance from the pubic bone to the uterus). fundus of the uterus).
From the 2nd month, every month the height of the uterus will increase by 4cm. Based on that, we can approximate the gestational age according to the formula:
Gestational age (in months) = (uterine height/4) + 1. Or estimate:
12 weeks pregnant, uterine height equivalent to about 1/3 above the pubic bone of the pregnant mother. At 16 weeks pregnant, the height of the uterus is equivalent to about 2/3 above the pubic bone of the pregnant mother. At 20 weeks pregnant, the uterine height is the same as the umbilicus at 24 weeks pregnant, the uterine height is a little higher than the navel 28 weeks old, the uterine height is 1/4 at the top of the abdomen, above the navel 32 weeks pregnant The uterus is 2/4 at the top of the abdomen, above the navel At 36 weeks of age, the height of the uterus is 3/4 at the top of the abdomen, above the navel.

Gestational age is one of the important factors in assessing fetal development. The methods of calculating gestational age may deviate slightly from reality but will not be too large. Knowing the exact gestational age helps you to be proactive in the process of taking care of yourself and your baby. Therefore, you should go to the doctor and monitor your pregnancy periodically during pregnancy.
Maternity care package package at Vinmec International General Hospital always provides pregnant mothers with full benefits of examination, 2D, 4D ultrasound so that mothers can always monitor the development of the fetus. as well as the most accurate gestational age and date of birth.
Dr. Tuyet Mai has over 30 years of experience in examination and treatment in the field of Obstetrics and Gynecology, especially in lower-line surgery, family planning, specialized laparoscopic surgery, and multi-surgery management. severe and difficult such as:
Hysterectomy, hymenectomy Surgery for uterine fibroids, cervical cancer Cervical cancer vaccination Cervical cancer early detection Cervical electrocautery Examination and treatment endocrine therapy