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How to Correctly Calculate Pregnancy

It is important for pregnant women to calculate their gestational age in order to better know the development of their womb. Usually, pregnant women will consult a midwife or doctor to obtain information about gestational age and the health of the fetus. Through this examination, pregnant women can gain a clearer understanding of their gestational age and the health condition of the fetus they are carrying.

This is How to Calculate Gestational Age

Knowing the gestational age is very important, you know! By knowing the gestational age, we can estimate when the baby will be born. Well, usually the baby's birth date falls around two weeks before or two weeks after the predetermined expected date of birth (HPL). For those of you who want to know how to calculate gestational age, let's look at the following steps:

1. Based on the first day of the last menstruation (HPHT)

One popular way to calculate gestational age is to determine the date of your last menstrual period before becoming pregnant. This method is known as Naegele's formula and is considered the best method for women who have regular menstrual cycles of 28 days.

To use this method, the first step is to determine the date of the HPHT (First Day of Last Menstruation). After that, add 40 weeks to that date to get the estimated due date. The assumption is that pregnancy usually lasts 9 months or about 40 weeks, which is equivalent to 280 days. By knowing the estimated day of birth, we can determine the gestational age. The following is a simulation of the calculation:

  • Determine the HPHT date.
  • Add one year to the date.
  • Add seven days.
  • Rewind three months.

For example, if your HPHT is July 22, 2022, then the calculation is as follows:

July 22, 2022 + 1 year = July 22, 2023

22 July 2023 + 7 days = 29 July 2023

29 July 2023 - 3 months = 29 April 2023

Based on this formula, the estimated day of your baby's birth is April 29, 2023. Although this method is quite easy and accurate, keep in mind that this method cannot be used by women who don't remember the date of their HPHT or have irregular menstrual cycles.

2. Based on ultrasound

If the previous method is considered not to provide accurate results, for example if your menstruation is irregular, you can visit a doctor to find out the gestational age with more certainty. The obstetrician will perform a physical examination and transvaginal ultrasound to determine the gestational age more accurately.

In early pregnancy, ultrasound results will be more accurate in calculating gestational age. This is because in the first few weeks, fetal development usually proceeds at the same rate.

However, over time, fetal growth can vary. There are months where growth is fast, and other months it can slow down. Therefore, an ultrasound examination performed in the last trimester of pregnancy is not to determine the age of the fetus, but to monitor whether the growth of the fetus is going well.

Benefits of Calculating Early Pregnancy Age

Expectant mothers can also calculate their own gestational age, not only doctors, midwives, or nurses know how. Calculating gestational age from the start has significant benefits, such as:

  • Knowing the ongoing gestational age.
  • Monitoring fetal development better.
  • Detecting any problems in the fetus more quickly.
  • Knowing the baby's weight according to gestational age.
  • Estimating the baby's due date.

Calculating gestational age is indeed important to determine the time of birth of the baby. There are two general methods used, namely calculating the First Day of Last Menstruation (HPHT) and ultrasound examination (USG). However, the results of these two methods may not always be the same, because they have different conditions for achieving accurate results.

You don't need to worry, the obstetrician will always monitor the progress of your pregnancy and let you know when your baby will be born. This is why it is important to have regular prenatal checkups with your obstetrician.


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