There are still many women who do not know how to calculate gestational age. Although it is difficult to determine accurately because we cannot know exactly when fertilization occurs, gestational age can be estimated in several ways.
To calculate gestational age, the method that is widely used today is based on the date of the last menstrual period. The first day of the last menstrual period (LMP) is considered the first day of gestation.
Usually a woman will undergo a pregnancy of about 280 days or 40 weeks from HPHT. The assumption that HPHT is the first day of pregnancy is still considered quite accurate, although fertilization usually begins to occur around 11-21 days after that date.
This is how to calculate gestational age
Knowing the gestational age is very important to estimate the time of birth. When the due date (HPL) has been determined, the baby's due date is between two weeks before and two weeks after the HPL.
To find out how to calculate gestational age, the following steps can be taken:
Based on the first day of the last menstrual period (LMP)
A popular way to calculate gestational age is to determine the date of your last menstrual period before becoming pregnant. This method is known as the Naegele formula. This method is considered best for women who have a regular 28-day menstrual cycle.
First, determine the date of LMP and then add 40 weeks from that date to determine the approximate day of delivery. This is based on the assumption that pregnancy is usually carried out for 9 months or 40 weeks or 280 days. By knowing the estimated date of birth of the baby, the gestational age can be known.
The following is the calculation simulation:
- Determine the first day of the last menstrual period (LMP)
- Add one year
- Add seven days
- Move back three months
So if the HPHT is dated July 22 2018, the calculation becomes:
- 22 July 2018 + 1 year = 22 July 2019
- 22 July 2019 + 7 days = 29 July 2019
- 29 July 2019 - 3 months = 29 April 2019
Based on this formula, the interpretation of the baby's birth day is April 29, 2019.
Although easy and fairly accurate, this method cannot be applied to women who do not remember when their HPHT was or who have irregular menstrual cycles.
Based on ultrasound
In situations where the above method is considered not to give accurate results, for example if your period is irregular, you can visit a doctor to determine the gestational age. The obstetrician will perform a physical examination and a transvaginal ultrasound to determine the gestational age more accurately.
Ultrasound results in calculating gestational age are more accurate if done in the early days of pregnancy. This is because in the first few weeks, the fetus tends to develop at the same rate.
However, as gestational age increases, the rate of fetal growth can vary. Growth can be fast in certain months, but can slow down in the following months. Therefore, ultrasound examinations performed in the last trimester of pregnancy are not intended to determine the age of the fetus, but to monitor whether the fetus is growing well.
Calculating gestational age is important to estimate the time of birth of the baby. The most commonly used methods are HPHT calculations and ultrasound examinations. However, the results of the two may not be the same, because each has different conditions for obtaining accurate results.
But don't worry, the obstetrician will continue to monitor your pregnancy and let you know when your little one is about to be born. That is why, regular pregnancy check-ups to the obstetrician need to be done. When you consult a doctor, you can also ask your doctor for advice regarding things to avoid during late pregnancy.