The Correct Way to Calculate Pregnancy (Gestational age)

All pregnant women want to know the correct way to calculate Gestational age. In this article, we will explain it in detail, along with other important information.

The Correct Way to Calculate Gestational age

The full pregnancy period lasts 280 days, 40 weeks, or a little over 9 months, divided into 3 trimesters. Here is the correct way to calculate Gestational age:

• The Correct Way To Calculate Pregnancy By Weeks

The correct way to calculate Gestational age is based on knowing the date of the first day of your last menstrual period (LMP). From this date, you calculate the number of weeks and days until the current day, and the result is the gestational age. 

For example, if today is January 18th and your last period was on December 5th, the duration between these dates is 44 days, meaning the pregnancy is approximately six weeks and two days.

Although this method might be slightly confusing because it counts from the last menstrual period, which was several weeks before actual conception, it is based on the start of the menstrual cycle that released the egg that was fertilized.

It is difficult to pinpoint the exact date of ovulation and fertilization since ovulation usually occurs two weeks after the menstrual period, but the exact date may vary, even in regular cycles.

It’s worth noting that many online websites and apps offer pregnancy calculators, where you simply input the date of the first day of your last period (LMP).

• The Correct Way to Calculate Pregnancy By Months

In reality, a typical month is 30 or 31 days long, except for February, which has 28 days. This means a month equals 4 weeks and 3 days, not exactly 4 weeks.

Therefore, when calculating pregnancy in months, not all months will be exactly 4 weeks. Some months will be counted as 4 weeks, while others will be counted as 5 weeks.

In general, after calculating the Gestational age in weeks, you can use the following table to convert it to months:

Other Ways to Calculate Gestational age

In addition to the correct methods of calculating Gestational age in weeks and months that we previously mentioned, there are several other methods you can use to calculate gestational age, either manually or with the help of technology and tools:

• The 4 ⅓ Method

This is another manual method to calculate the gestational age, using the following formula: “Gestational age = (current date - last menstrual period) * 4 ⅓.”

It’s important to note that days are subtracted from days, and months from months, with the multiplication by 4 ⅓ only applied to the months.

For example, if today's date is 14/07/2024 and the last period was 07/04/2024, the process is as follows:

1. Gestational age = (14-07) (07-04) * 4 ⅓
2. Gestational age = (7) days and (3 months) * 4 ⅓
3. Gestational age = 7 days and 13 weeks, which means 14 weeks or 4 months.

• Ultrasound Scan

There are two types of ultrasound scans: the vaginal ultrasound, typically performed in the early stages of pregnancy, and the abdominal ultrasound.

In general, an ultrasound helps accurately estimate gestational age up to 95%. It can also determine the baby’s gender, check the development of the uterus, monitor the baby’s growth and health, and predict the expected due date.

This method is particularly useful for women who don’t remember the date of their last period.

• Detecting Fetal Movement

Compared to other methods, this one is less accurate because it relies on detecting fetal movements. It can also be challenging for first-time mothers, but it may be slightly easier for women who have been pregnant before, as they are more familiar with recognizing fetal movements in the womb.

The method is based on observing fetal movements, as they typically begin around 18-20 weeks in a first pregnancy. In subsequent pregnancies, movements may begin earlier, around 16-18 weeks.

• Pregnancy Hormone Levels

A doctor can estimate the gestational age based on the levels of the pregnancy hormone (hCG). This hormone is released after the fertilized egg implants in the uterus, and its levels increase rapidly in the early weeks of pregnancy.

Blazma offers a Beta-hCG test, which does not require fasting or any other special conditions.