Calculating Corrected Age of Premature Babies

For a baby to be considered “full-term”, she needs to be in gestation for a total of 40 weeks.  Some sources state 39 weeks is full-term, but for simplicity sake, we’ll just use 40 weeks.  Gestation refers to the period of time between conception and birth when a baby is growing in mother’s womb, and this period of time is called gestational age.

 

A baby who was born at 40 weeks gestation (full-term), goes by one age:  chronological age.  The chronological age is the amount of time since birth, usually expressed as months, weeks, or days.

 

A baby born prior to 40 weeks gestation (known as premature babies or preemies) may be referred to by two ages:  chronological age and corrected (or adjusted) age.  The corrected age is the age based on baby’s due date.

 

Sample Calculation

A baby girl was born 34 weeks gestation.  She is 4 months old.  What is her corrected age?

 

Calculating a baby’s corrected age is pretty easy and straightforward.  The first step is to determine the amount of time premature the baby is by subtracting the gestational age in weeks from 40 weeks for a full-term pregnancy:

Weeks premature = 40 weeks for full-term – gestational age in weeks

Weeks premature = 40 weeks for full-term – 34 weeks gestational age

Weeks premature = 6 weeks

 

The second step is calculating baby’s corrected age by simply subtracting the number of weeks premature from her chronological age:

Corrected age = chronological age in weeks – number of weeks premature

Corrected age = 16 weeks (which is 4 months expressed in weeks) – 6 weeks premature

Corrected age = 10 weeks

 

We could leave it as 10 weeks corrected age, or we can convert this into corrected age in months by dividing the corrected age in weeks by 4 weeks per month:

Corrected age (months) = 10 weeks corrected age / 4 weeks per month

Corrected age (months) = 2.5 months

 

Final Thoughts on Corrected Age

Parents of a premature baby might get frustrated at times, especially if they speak with other parents with similarly aged babies or have been reading books on the various developmental stages their baby should be progressing through.  A 4-month old baby with a corrected age of 2.5 months will most likely not have the same developmental skills of a full-term 4-month old baby.  Parents should be made aware of this and also informed that the delay in developmental skills is only temporary.  Many children catch-up to their full-term counterparts within 2 to 3 years.

 

The chart below shows some of the developmental stages of a 4-month old with corrected age of 2.5 months and that of a full-term 4-month old for comparison.

4-Month Old, Corrected Age of 2.5 Mos
4-Month Old, Full-Term
  • Acquiring strength in her neck and begins to hold her head a little steadier while lying on her belly or being supported upright
  • Suckling on her fingers
  • Briefly holding a toy placed in her hands
  • Sleeps sporadically throughout the day, but rarely throughout the night
  • Can see objects only closely, about 18 inches away
  • Smiling and laughing
  • Consuming only breastmilk and/or infant formula
  • The number of bowel movements will start to lessen

 

 

 

  • Raise herself up on her arms when placed on her belly
  • Keep her head propped up while in a sitting position
  • Pick her head up off the floor while on her belly
  • Kick and push with her feet
  • Roll over
  • Reach for objects and place objects in her mouth
  • Play with her toes
  • Make babbling noises and laughs
  • Her face shows more emotions
  • Her eyes move smoothly and follow objects and people around the room
  • Can see objects farther away
  • Sits unassisted (more advanced)
  • Stands while holding onto something or someone (more advanced)
  • May be starting on single grain cereals