A google search reveals that premature babies take around 3 years to catch up, but a premature baby is obviously not born more than a couple months earlier than they “should” be. Why does it take so long for them to develop, why wouldn’t they just continue growing as they would have inside the womb?
Thoes ‘couple of months’ are extremely important. (Remember that a whole pregnancy is not even a year). And we cannot (yet) reproduce the womb conditions.
So in conclusion as of right now, is actually a miracle we can keep the babies alive .
If you go based on how long it’s been from time of conception, a premature baby is literally younger than a full term baby for the rest of their lives. In babies there is a huge difference between a 4 month old and a 6 month old, so they will naturally be way behind if they are 8 weeks premature. This sort of dissipates over time bc there isn’t much difference between a 5 year old and a 5 year 2 month old.
Also the womb is the perfect environment for a growing baby. Once outside the womb a newborn premature baby will not develop as quickly.
My friend had a baby at 11 weeks early and it then took 20 weeks till they could take him home (2 months past his original due date). So he was 5 months old, maybe 6-8 lbs, and he was not as healthy as a normal newborn, he was on oxygen and had other issues. So physically he was like 5 months behind other kids his age and it took a while to catch up and for the difference be less noticeable.
Consider that a baby has every incentive to grow as fast as physically possible. If a baby could “catch up” it would mean other babies aren’t doing their best. Which they are.
The lungs typically suffer in premature births. With dodgy lungs the child has to work harder to breathe for the first few years (or longer), this extra energy requirement causes them to grow slower. Also consider there’s normally a reason why the child is born early – like growth restriction.