Premature babies have both an adjusted age and an actual, or birth, age. Actual/birth age is simply the age a baby is based on his birthday. A baby born on January 20th turns 1-year on the next January 20th; that's his birthday.
Adjusted age is the age a baby would be based on his due date. For example, let's consider a baby that was due on February 20th, but was born a month early on January 20th. Come March 20th, his actual/birth age will be 2-months old because 2 months have past since he was born. However, his adjusted age is only 1-month old, because only 1 month has past since his due date. His adjusted age will be about 1-month behind because he was born a month early. Babies born on or after their due date do not have an adjusted age.
Why does adjusted age matter?
Experts have found that a baby's development more closely follows his adjusted age rather than his birth age. When a baby is born premature, there is some development that would've happened inside the womb that now needs to happen outside the womb. This can mean that some development happens slightly later than the "normal" age. However, this does not mean the baby is behind in development. It just means he was born ahead of normal newborn development, and therefore needs some time to catch up.
Regarding sleep, adjusted age mostly impacts wake windows and the number of naps a baby needs. For example, a 4-month old baby can normally handle wake windows of about 2 hours. However, if a 4-month old baby is only 3 months adjusted, then he may only be able to handle wake windows of about 1.5 hours. Similarly, the transition from 3 naps down to 2 naps normally happens between 6-8 months. However, for a baby who is adjusted 1-month behind, this transition may not happen until between 7-9 months.
Adjusted age can also affect when a baby reaches milestones, like rolling, sitting unassisted, and walking. Therefore, common sleep regressions may also happen a bit later for an adjusted baby.
When does adjusted age NOT matter?
Typically, I don't take adjusted age into account with sleep unless it is more than two weeks different from baby's birth age. If a baby was born within two weeks of his due date, I don't find that to be enough of an age gap to really affect wake windows and naps that much. Wake windows are meant to be a guideline anyway.
On the other end of things, experts believe most premature babies will "catch up" to their birth age by 1 year of age, in terms of development. So, when a client comes to me with a toddler or preschooler, I'm not quite as conservative when considering their adjusted age in my recommendations as I would be with a younger baby, unless their age gap was significant.
If you have a premature baby, download my free Sleep Times Chart and take your baby's adjusted age into consideration. Contact me if you need help figuring out the appropriate wake windows for your baby!
~Ashley Bell, pediatric sleep consultant