Calculating the Pregnancy Weeks (gestational age) is essential to more accurately assess the health of the mother and fetus and understand the changes that occur to the mother during this period. Find out more information about gestational age and how to calculate it by reading the following article.


Gestational age A normal pregnancy lasts 280 days (40 weeks) when counting from the first day of the last menstrual period, or 266 days (38 weeks) when counting from the date of ovulation (the expected date of conception). In general, most doctors count from the last menstrual period.


The following table shows pregnancy in weeks and months: (5)


Pregnancy month

Weeks

First month

1 - 4

Second month

5 - 8

Third month

9 - 13

Fourth month

14 - 17

Fifth month

18 - 22

Sixth month

23 - 27

Seventh month

28 - 31

Eighth month

32 - 35

Ninth month

36 - 40


How can gestational age be calculated?

There are two main ways to calculate gestational age:

1-     Based on the date of the last menstrual period

(if the menstrual cycle is regular) it is the most widely used method among doctors. Doctors start counting the weeks that have passed from the first day of your last menstrual period. (1) (2)



You can calculate the number of weeks yourself in simple ways, such as: (1)

1.Get a pen, paper, and calendar, and count the weeks from the date of the first day of your last menstrual period until today’s date.

2.Use one of the pregnancy calculators available on the Internet, and enter the date of the first day of your last menstrual period.

3.Count the number of days from the date of the first day of the last menstrual period until today’s date and divide it by 7, to get the number of weeks that have passed.


Here's a practical example of how to calculate yourself:

If the date of the first day of your last menstrual period is 17-7-2023 and today’s date is 19-2-2024, then the number of days during this period is 218 days. Dividing it by 7 means the number of weeks of pregnancy is 31 weeks and one day.






You should know that calculating the gestational age always gives estimated numbers, and that a normal pregnancy lasts approximately 40 weeks, and it can vary by two weeks.





2-Abdominal ultrasound

It is the most accurate method for calculating the gestational age and the estimated date of delivery and is used especially in cases of irregular menstruation. During which the length of the fetus is measured from the top of the head to the buttocks, which is known as the Crown-rump length (CRL), and accordingly, the weeks of pregnancy are determined more accurately. (3)

How do I calculate the estimated date of delivery (EDD)?

The estimated date of delivery is calculated if your menstrual cycle is regular based on Naegele's Rule, which includes: (4)


1. Determine the first day of your last menstrual period.

2. Add 7 days to the number of days from the date of the last menstrual period.

3. Subtract 3 months from the number of months.

4. Add a year to that date.


For example, if the date of the last menstrual period is 17-7-2023 as in the previous example, the estimated date of delivery is calculated as follows:

1. We add 7 days to today's date (17) = 24

2. We subtract 3 months from the current month, which is (7) = 4

3. We add a year to the years = 2024


Therefore, the estimated date of delivery will be 24\4\2024. Remember that this date is an estimate, and you may give birth several days before or after it.





Preparing for motherhood? Trust Al-Ahli Hospital’s Obstetrics and Gynecology Department to provide expert care and personalized support throughout your pregnancy journey. Our experienced medical team is dedicated to ensuring a safe, comfortable, and healthy experience for every mother-to-be.




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