Why is it important?

Brain development doesn’t speed up when a baby is born early; it needs the same amount of time to grow as a baby growing inside their mother. For example, a baby born at 28 weeks gestation will need an additional full 12 weeks of growth and development before they could be expected to act like a newborn baby who had a full 40 weeks gestation. That is why the developmental milestones for a premature baby are based on corrected gestational age rather than chronological age. Babies born early will be also be physically smaller so your premature baby’s growth should be plotted on the growth curve at the corrected gestational age.

How is corrected age calculated?

To calculate your baby’s corrected gestational age, start with your baby’s chronological age in weeks or months, then subtract the number of weeks your baby was born prematurely. For example, if your baby was born 12 weeks ago and was 4 weeks early (based on your due date), your baby’s corrected gestational age is 8 weeks (2 months):

12 weeks – 4 weeks = 8 weeks.

How long to use the corrected age?

Most babies will begin to “catch up” in growth and development to near their chronological age by the end of the first year. There continues to be catch up growth and development, particularly for those babies born extremely early, at least until 3 years of age. Some research shows catch up growth and development continuing into adolescence!

Premature and newborn brains are especially fragile because of how quickly and intricately they develop in the third trimester of pregnancy and right after birth. This also makes the brain especially responsive to a developmentally-supportive environment. For babies who have had brain injury due to their preterm birth, the brain can adapt and develop to “rewire” around the injured areas. This is referred to as “brain plasticity” and is a unique characteristic of newborns that doesn’t happen with brain injuries of older children and adults. Because of brain plasticity, it is sometimes hard to predict how a baby will adapt to preterm brain injury. Importantly, it also means that caring parents and positive developmental experiences can play a very big role in recovery from brain injury or from the stress of being born early.

What to say when people ask “How old is your baby?”

Like many parents, you may find it difficult to know what to say when people see your baby and ask how old he is, because it can be complicated to explain in casual everyday conversation.

Parents of premature babies often choose to use the corrected age when they talk with acquaintances, particularly for the first few months after going home as it reminds everyone not to expect your baby to look or act older than their corrected age. Those few months will quickly start making less and less of a difference as your baby gets older. Over time you may start saying your baby’s chronological age when asked how old they are. However, you still may get uninvited comments about how small your baby is for their age – you know how people are….