Premature Babies Age Corrected & Chronological

Premature babies have two ages

Getting your baby’s age right is simple. Right?

Normally yes, however when working with babies born prematurely even professionals sometimes get it.

Normally you just count the number of months, weeks and days from your baby’s date of birth to determine his or her age. However the age of premature baby is work out a little differently.

Gestational age
Image via Wikipedia

In fact, premature babies have two ages…

  1. Chronological or Calendar age and
  2. Corrected age

Your baby’s calendar age

Calendar age is your child’s age calculated on his date of birth. As far as everyone is concerned, your baby only has this one age. That is the age that goes onto every imaginable form and paperwork during his or her lifetime.

But before we go to the second age, let’s first look at what qualifies as a premature baby.

What is a premature baby?

Full term pregnancy is accepted to be 40 weeks from the mother’s last menstrual period. So, all babies have a normal 40-week development period before birth.

And any baby born before 37 full development weeks is seen as a premature baby.

What this simply means is that if two babies are born on the same day, but did not have the same development period in the womb, their developments would not be the same. In fact, not even closely similar.

Say baby Clint was a full term 40-week baby, where as baby Sky was born at 35 weeks. Both of them were born on 28th January. Now, on 28th June both of them are 6 months old. Clint is sitting unaided, but Sky shows no signs of sitting whatsoever.

It is important to realise that Sky was actually born 5 weeks ahead of schedule. Sky should have been born around the 4th March. So on 28th January Sky started off with a stumbling block… she did not have the full period to fully develop in the womb.

Because of this shorter development period, Sky is slightly smaller than Clint. A further impediment for a premature baby like Sky is that she initially grows and develops at a slower rate than Clint.

At this stage you will agree that as long as you keep comparing Sky and Clint’s development, Sky will in all likelihood always be behind… at least for the first two years.

Calculating the second age

One way of realistically determining how well Sky is developing is to use Corrected Age (CA). Quite often this is also known as Gestationally Corrected Age (GCA) or sometimes just Gestational Age (GA).

All these terms are based on the age the premature baby would be if the pregnancy had been 40 weeks. It is a calculated age to compensate for a premature baby’s shorter development period in the womb.

CA (weeks or months) = calendar age (weeks or months) – period prematurely born (weeks or months)

If we now look at Sky, her corrected age on 28th June is 6 months (on 28th June) minus 1.15 months (born 5 weeks prematurely) = 4.85 months

(This is based on 52 weeks per year, which is an average of 41/3 weeks per calendar month.  As we are aware some months have more days than others and so using the average is a close approximation that is accurate enough for the purposes of this calculation and the single day of a year or two in the case of a leap year are removed from the calculations altogether)

52 weeks = 364 days! = 12 months

One month = 52/12 weeks = 41/3 weeks

Therefore 5 weeks = 5¸41/3 months = 1.15 months (to two decimal places)

Using Sky’s CA immediately means that you don’t expect Sky to do the same things that Clint can already do. The fact that Sky is not sitting on 28th June is therefore not yet a concern.

One warning about using CA

It only works for babies born before 37 weeks. It does not apply to babies born close to the 40-week full term development period.

For premature baby clothes and personalised baby gifts please visit  prem2pram

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  1. Trackback: Tweets that mention Premature Babies Age Corrected & Chronological « Prem2Pram – Premature Baby Blog -- Topsy.com

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