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Adjusted Ages for Twins: What They Mean and How To Calculate Them

Understanding adjusted ages for twins and how to calculate twins’ adjusted age

If you hang around with twin moms long enough you will hear things like, ‘They’re 5 months, 3.5 months old adjusted.’

What in the world does that mean? Aren’t babies one age, not two? Why were two ages given and what do you do with that information?

Welcome to the world of adjusted ages. Adjusted ages are when you take into account that a baby was born prematurely when considering milestones and overall development.

Twins are often born early, so adjusted ages are commonly used. They can be a bit confusing though. This post will walk you through what an adjusted age is, when they are used, and how to calculate the adjusted age with twins.

Newborn twins

Adjusted Ages for Twins

Having twins throws you into a whole new world. The world of being a mom of multiples.

In some ways, it is no different than being a parent to a singleton. Sure, you have two babies. But babies are babies, their needs are all basically the same.

But in other ways, it is a whole new ballgame (besides just using the word singleton now). Somehow two babies add up to so much more. And one thing to keep in mind during your pregnancy through the baby years is the adjusted age of your twins.

What Is an Adjusted Age?

Adjusted age is when you take into account that your twins were born early. When babies are born prematurely they miss time in the womb when they would be developing. As a result, they need to make up this time after birth.

Once they have had that developmental time they can start to work on skills that babies develop as they age.

Why Use an Adjusted Age?

Short answer? Adjusted ages give a more accurate picture of where your twins should be in terms of development taking into account the fact that they were born early.

For example, four month old babies usually have pretty good head control. But if your twins were born 8 weeks early, they might still be a bit wobbly at 4 months. This makes sense, they missed out on 8 weeks of development inside the womb.

In terms of overall existence, your 8 week early twins have had 8 fewer weeks to grow and get strong. It is unrealistic to think they will be at the same developmental points as a baby who has had those extra 8 weeks.

Adjusted ages are just used to take into account the fact that your premature babies had less time in the womb to develop. Using an adjusted age gives a more realistic timeline for hitting milestones.

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When To Use Adjusted Age

Adjusted age is used when looking at common milestones babies reach. These include, but are not limited to:

  1. Sleeping through the night
  2. Holding up the head
  3. Smiling
  4. Rolling
  5. Sitting up
  6. Grabbing items
  7. Crawling
  8. Walking
  9. Cooing

You get the point. Every step can be pushed back for the first few years.

How To Calculate Adjusted Age

Adjusted age is actually pretty easy to calculate. Take your twins’ actual age and subtract the number of weeks premature they were.

Adjusted Age Calculation

Actual Age – Weeks Premature = Adjusted Age

Here is an example. If your baby was born at 32 weeks, they were born 8 weeks early. So when their actual age is 16 weeks, the equation would look like this:

16 weeks (actual age) – 8 weeks (premature) = 8 weeks (adjusted age)

While this baby is almost 4 months old, you would expect them to be hitting 2 month old milestones.

Calculating Adjusted Ages for Twins

Of course, when you add another baby into the mix things just get more complicated. Twins don’t always have the same straightforward calculation that singletons do.

Why is that? Because twins don’t have the same clear cut timeline to be considered full term.

Singleton pregnancies pretty much stick to the 40-week model. 37-38 weeks is early term, 39-40 is term, and 41-42 is late term. But for adjusted age, 40 weeks is the given.

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Twins? There are more variables to take into account. What type of twins do you have? Sharing a placenta can change what is considered full term for your twins. (The placenta will tire out faster if it is supporting two babies.)

The general thought is that twins are considered full term at 37 weeks. This means if your baby was born at 32 weeks, they are only 5 weeks early. You subtract 5 weeks from their actual age to get their adjusted age.

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What Is Considered Full Term for Twins?

So how do you know which term length to use to calculate your twins’ adjusted age?

You will need to ask your doctor and your twins’ pediatrician. My twins were born at 36.5 weeks. They were Mo/Di, meaning they shared a placenta. Because of this my doctor and my twins’ pediatrician recommended going off of actual age in terms of meeting milestones. We used 37 weeks as our full term pregnancy length.

Your doctors will know best based off what they have seen from other patients and what they know about your pregnancy. So talk to your doctors to determine if an adjusted age calculation is needed.

Do Twins Meet All Milestones Late?

While adjusted age can be helpful in understanding why twins might hit milestones late, it is important to remember they might not. Your twins might hit some milestones ‘on time’ and others late, just like full term babies.

There are a lot of factors that go into milestones and there are ranges for what is considered ‘normal.’ As your twins get older the corrected age may become less and less of a factor too.

Remember that your twins are individuals and will not hit every milestone at the same time.

If you have concerns about how your twins are developing you need to talk to their pediatrician about it. (And speak up! You are your twins’ best advocate.)

How Long Do You Use Adjusted Age?

How long do you need to take into account the adjusted age? Don’t worry, the corrected age isn’t something you need to use forever.

Generally, your twins will have ‘caught up’ by about 2.5 years old. So between 2 and 3 years old adjusted age isn’t really an issue anymore.

How To Calculate Adjusted Ages for Twins

Corrected Ages For Twins

Using a corrected age is important in terms of understanding when your wins will reach developmental milestones in the first few years. But it isn’t a black and white issue. Talk to your medical professionals to get a better picture of how you should calculate your twins’ adjusted ages and when to use them.


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