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If you are pregnant and need to calculate the gestational age of your fetus and understand what is gestational age, then read on.

What is gestational age?

Once you start attending a medical practitioner and going for early pregnancy scans, you will hear the term gestational age. If it is your first pregnancy you may not be familiar with what this means.

Simply it is the term used medically to calculate how far along your pregnancy is. It is calculated in weeks, and measured from the first day of your last menstrual cycle to today’s date, or the day of your appointment.

How ultrasound scans can measure gestational age

gestational age and birth weight chart

Of course not all of us keep track of our first day of menstruation religiously. So what happens in these common cases? When you come for an ultrasound pregnancy scan, the sonographer will be able to tell the gestational age of your fetus.

This is calculated by measuring the diameter of the gestational sac or CRL – the length of the fetal pole. If you’re curious about how we do this during your ultrasound scan, here are some example of the formula:

We take the mm measurements of your fetus’ gestational sac and add this to 4 weeks/28 days. This gives you a general estimate of gestational age. So for example if the sac measures 5mm, we add this to 28 and get a total of 33 days, which would be 4 weeks and 5 days in total. Also charts have been developed to illustrate and calculate this.

What is a pregnancy wheel?

A pregnancy wheel is a small circular calendar that is also referred to a gestation calculator. By using your LMP – last menstrual period, the pregnancy wheel can calculate your estimated due date. Simple move its pointer to your LMP rotating the wheel to show the estimated due date.


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All articles on the blog and website are intended as information only. Please do not consider any of the information provided here as a substitute for medical advice. At all times seek medical advice directly with your own doctor and medical team.