Gestational Age: What it Means

Team Peanut
Team Peanutover 1 year ago4 min read

What is gestation? Well, gestation is essentially the amount of time between when you conceive and when you give birth. So, when we talk about gestational age, we mean how far along a pregnancy is.

Gestational Age

Knowing the gestational age of your baby helps your doctor to estimate your due date. And it gives them a guideline for working out if your little one is growing as they should be.

So, let’s find out more.

In this article: 📝

  • How do you calculate gestational age?
  • What is the difference between gestational age and fetal age?
  • What is a “normal” gestational age?
  • Why is gestational age important?
  • Can you calculate gestational age when your baby arrives?
  • One last word on gestational age

How do you calculate gestational age?

To work out the gestational age of your baby, your doctor can use a combination of: the date of your last period and a first trimester ultrasound (also called the “dating” ultrasound!). They’ll describe your baby’s gestational age in weeks and days – for example, 23 weeks and 4 days.

By the way, there are also handy apps and online tools that you can use yourself as a guide to gestational age. That is, when you’ve just found out you’re pregnant and you haven’t seen your doctor yet. Just tap it into your browser search, and you can try out a few.

Things are a little different if you’ve conceived via IVF or another form of ART (assisted reproductive technology). In this case, the embryo’s age and the date of conception are used to calculate the gestational age instead. And because conception actually happened outside your body, under lab conditions, these calculations have a high level of accuracy.

The fertility team who helped on your pregnancy journey can use various formulas to calculate your baby’s gestational age, depending on the type of IVF you’ve had.

What is the difference between gestational age and fetal age?

Gestational age, as we’ve seen, is worked out from the date of your last period. It’s the number most of us use to describe how long a pregnancy is.

As in “I’ve hit 35 weeks – nearly there!”

But fetal age is different: it’s actually two weeks behind gestational age. That’s because it starts at the time of conception, and conception happens around ovulation (about two weeks after your last period). So fetal age specifically tells you the age of the fetus – it’s your baby’s actual age.

What is a “normal” gestational age?

On average, the gestational period lasts between 37 and 42 weeks. So, gestational age is key to tracking where you are on your pregnancy journey.

Why is gestational age important?

Gestational age is important because it can help your healthcare practitioner work out if your baby is growing as they need to. If your baby seems to be growing differently to their gestational age, they may need extra monitoring. Gestational age also helps doctors to know when to do any prenatal tests and screenings.

Can you calculate gestational age when your baby arrives?

When your baby is born, your healthcare practitioner will carry out some health checks, and they’ll also check your baby’s gestational age. To do this, they’ll look at some key things, like your baby’s length, weight, head circumference, skin condition, and vital signs. They’ll also consider the condition of their hair, muscle tone, posture, and reflexes.

Depending on their results, your baby will be noted as: “appropriate for gestational age” (AGA), “small for gestational age” (SGA), or “large for gestational age” (LGA). If they’re “small” or “large” that just means that your healthcare practitioner will keep an extra eye on them, in case of complications.

One last word on gestational age

Because calculating your due date from your last period isn’t always accurate, confirming gestational age from an ultrasound in your first trimester can be really useful. Saying that, it’s possible that your due date could actually be changed later on in pregnancy by your healthcare practitioner.

But, essentially, the more information you have and the more accurate it is, the more you’ll know what to expect for each milestone of your pregnancy.

Why not connect with other mamas-to-be on Peanut who are due around the same time as you and share those milestones together?

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