Do Premature Babies Catch Up? What the Research Shows

§I.What the large studies found, by birth week

About 1 in 10 babies in the United States is born before 37 weeks (10.41% in 2023)¹⁸, and about 7 in 10 of them arrive at 34 to 36 weeks¹⁹. The table follows children from France’s national EPIPAGE-2 study, which followed babies born at 22 to 34 weeks in 2011 to age 5½^1,2, and from UK studies of babies born at 32 to 36 weeks^4,5.

A questionnaire flag means the Ages and Stages Questionnaire, filled in by parents, suggested a closer look at one or more areas. It is not a diagnosis. A moderate or severe difficulty means moderate or severe cerebral palsy, blindness or deafness, or a thinking-skills (IQ) score far below that of children born at term². Results at age 2 use corrected age.

Two things stand out. First, every group does better than the one born earlier. Second, “no difficulty at all” and “a moderate or severe difficulty” do not add up to 100: in each group, many children sit in between, with mild differences in movement, attention or learning that they live with well.

§II.Catching up runs on four clocks

Parents often picture catching up as one finish line. In the research it is at least four, and they run at different speeds:

• Growth. Weight, length and head size. Most babies grow faster than usual for a while after the NICU. For the smallest babies, weight can keep catching up into the teenage years.
• Milestones. Smiling, sitting, walking, babbling and first words, judged by corrected age until about age 2.
• School skills. Attention, reading, maths and how quickly a child takes in new information. Small differences can show up here even in children who met every early milestone.
• Adult life. Finishing school, work, independence and family. The long-term studies here are mostly reassuring.

A child can be fully caught up on one clock and a little behind on another, and that is common. It is one reason follow-up continues past the second birthday for babies born very early.

§III.Growth: weight and height catch up on their own timetable

Most babies born early grow faster than usual for a while after they go home, which doctors call catch-up growth. Your baby’s team plots it using corrected age, so a smaller number than a term-born baby with the same birthday is expected at first.

For the smallest babies the timetable is longer. In a Canadian study that followed babies born under 1,000 grams (about 2 pounds 3 ounces) into their twenties, weight fell further behind until about age 3, then caught up through the teenage years. By adulthood their body mass index matched their peers’, though on average they stayed a little shorter than their peers and than their parents’ heights would predict¹³. In a Cleveland study of babies born under 1,500 grams, girls had caught up in size by age 20, mostly between ages 8 and 20, while boys on average had not¹⁴.

At home, a growth curve that keeps climbing along its own line matters more than any single weigh-in. Ask your pediatrician to show you the curve, and raise feeding struggles or a curve that flattens.

§IV.Milestones: compare with corrected age until about 2

Until about age 2, compare your baby with babies of the same corrected age, not the same birthday. A baby born at 32 weeks arrived 8 weeks early, so 6 months after birth they are about 4 months corrected, and 4-month milestones are the fair comparison. Our guide to corrected age shows the formula and when to stop using it.

Then use the milestone guides for your baby’s corrected age, such as 18-month milestones, 2-year milestones and speech and language milestones, or the free Child Development Milestones Checker, which has a born-early option.

A milestone reached a little late, with steady progress, is a different picture from no progress or a lost skill. The first is common after an early birth. The second always deserves a call to your pediatrician.

§V.Born at 32 to 36 weeks: most catch up fully

This is the largest group by far: about 7 in 10 preterm babies are born at 34 to 36 weeks¹⁹, and many more at 32 or 33. Most of these babies catch up fully, and by school age most look like any of their classmates.

The research does show small differences across large groups. In the UK study of babies born at 32 to 36 weeks, 6 in 100 had a delay in thinking skills at age 2, against 2 in 100 born at term, and about 1.6 in 100 had a problem with movement, vision or hearing, against 0.3 in 100⁴. In England’s Millennium Cohort, 59 in 100 children born at 34 to 36 weeks had not reached a “good level” of development by the end of their first school year, against 51 in 100 born at term, and the authors noted that this gap was small next to other factors in a child’s life⁵. A Scottish study of more than 400,000 schoolchildren found that the chance of needing extra help at school rose a little with each week born earlier, even at 37 to 39 weeks⁶.

So for a baby born at 34, 35 or 36 weeks, the most likely outcome is a child who does well. It is still worth telling teachers about the early birth, and asking for a check if reading, attention or coordination seem harder than expected.

§VI.Born at 27 to 31 weeks: most do well, with more to watch

Babies born at 27 to 31 weeks usually spend weeks or months in the NICU, and their follow-up often continues for years. In EPIPAGE-2, about 4 in 100 had cerebral palsy at age 2¹. By age 5½, about 45 in 100 had no developmental difficulty at all, about 1 in 5 had a moderate or severe one, and the rest had mild difficulties^2,3, such as clumsiness, trouble with attention or thinking scores a little below average.

The week of birth is not the whole story. In a review of 71 studies, chronic lung disease of prematurity (bronchopulmonary dysplasia) explained much of the difference in average thinking scores between studies⁷. Ask your baby’s team which parts of the NICU stay matter most for your baby’s follow-up.

§VII.Born before 27 weeks: outcomes vary the most

These babies are the smallest and have the most to catch up on. In EPIPAGE-2, among children born at 24 to 26 weeks, about 7 in 100 had cerebral palsy at age 2 and about half had a questionnaire flag¹. By age 5½, about 1 in 3 had no developmental difficulty, a little over 1 in 4 had a moderate or severe one, and the rest had mild difficulties^2,3.

Across 71 studies of children born before 32 weeks, average IQ scores were about 13 points lower than those of children born at term, and the gap did not shrink for babies born from 1990 to 2008, despite better NICU care⁷. An average gap is not a ceiling: scores spread widely, so many children born this early still score in the average range.

For babies born at 22 or 23 weeks, most studies have too few children to give stable numbers. Your NICU follow-up team knows your baby’s history and is the best guide.

§VIII.School age and adult life

Attention and learning. Children born very early are more likely to be diagnosed with ADHD, at about 3 times the odds of children born at term in a review of 12 studies, and more for those born extremely early⁸. Autism is also more common: about 7 in 100 children in an 18-study review of babies born early, most of them around 28 weeks⁹, and about 6 in 100 when only full diagnostic assessments were counted¹⁰. Most children born early have neither, and the risk is highest for those born earliest.

Adult life. The longest follow-ups are reassuring about everyday life. In Canada, adults born under 1,000 grams in 1977 to 1982 were, at 22 to 25, about as likely as their peers to have finished school, found work, lived independently, married and had children¹². In Norway’s national registry of more than 900,000 births from 1967 to 1983, cerebral palsy was more common the earlier a baby was born: about 9 in 100 adults born at 23 to 27 weeks had it, against 1 in 1,000 born at term¹¹. So more than 9 in 10 of even the earliest-born survivors did not. NICU care has changed a great deal since then, so today’s babies may fare differently.

§IX.What helps a premature baby catch up

Keep every follow-up visit. Babies born before 32 weeks, or with complications, are usually seen in a NICU follow-up clinic. The American Academy of Pediatrics’ 2023 report asks pediatricians to sort babies born early by risk and to keep checking development through early childhood, not only until the first birthday¹⁷.

Ask for early intervention early. In the United States, any child under 3 can have a free early intervention evaluation, and you can contact your state’s program yourself, without a doctor’s referral. A Cochrane review of programs that start after the NICU found better thinking scores in the first years of life and a small benefit for movement in infancy; whether the gains last to school age is still unclear¹⁶. Our guide to early intervention evaluation walks through how to ask.

Talk, read and play every day. In a review of 31 studies of babies born very early, parents’ education predicted thinking skills more consistently than most NICU details, and family factors mattered more as children got older while NICU factors faded¹⁵. That does not mean a parent’s schooling decides a child’s future. It means the world a child grows up in keeps shaping development long after the NICU, and everyday conversation, books and play are part of that world.

Look after yourself too. NICU stays are hard on parents. If worry or sadness stays with you for weeks, tell your own doctor: it is common, and help works.

§X.Signs to raise with your pediatrician

You never need a reason from a list to ask. These signs are worth raising at the next visit, or sooner if they worry you:

• Not reaching milestones for your baby’s corrected age, or progress that seems to stall.
• Any skill your child had and has lost, at any age. Call promptly: prematurity does not explain a lost skill (see developmental regression).
• Using one hand much more than the other in the first year, or one side of the body seeming weaker¹⁷.
• Muscles that feel very stiff or very floppy, or legs that cross like scissors when your baby is held up.
• Not turning to voices or sounds, or not following faces and toys with the eyes.
• Few sounds, gestures or words compared with the speech milestones for corrected age.
• Feeding struggles, or a growth curve that flattens.

Bring both ages and a few written examples to the visit. Our guide to preparing for a pediatrician visit lists what to bring, and delay or normal variation? explains how doctors tell the two apart.