'When the Week Makes a Difference': What a Major Study Shows About the Link Between Gestational Age and Abilities at 9-10 Years

If a child is born significantly prematurely, this can affect their cognitive development many years later — and it’s not just about genetics. In a new study in JAMA Network Open, scientists analyzed data from 5,946 children from the large-scale ABCD project and found that those born at 32–33 weeks of pregnancy (moderate prematurity) often had lower scores on a number of cognitive tests at age 9–10. This effect persisted even after accounting for family income, pregnancy characteristics, and polygenic (genetic) indicators associated with learning ability and intelligence. The lowest scores were observed in children born at 32 weeks and earlier. But late preterm (34–36 weeks) and “early term” (37–38 weeks) babies were, on average, no different from their peers born at 39 weeks and later.

Why study this at all?

Premature birth is one of the key risk factors for health problems in childhood. The brain is intensively “built” between the 24th and 40th weeks: white and gray matter matures, connections are formed that will ensure speech, memory, attention. An early start can interrupt these processes. Dozens of studies have previously confirmed this, but they had two “bottlenecks”:

1. focus on extremely or very early prematurity, while the majority of preterm births occur at 32–36 weeks;
2. weak consideration of genetic differences between children. But genes significantly influence abilities: some children are born with a higher “setting” for learning, some with a lower one.

The new paper closes both gaps by comparing groups across a wide range of gestational ages and simultaneously subtracting the contribution of genetics using polygenic scores (PGS).

How the study was conducted

• Data source: Adolescent Brain Cognitive Development (ABCD) Study: US national cohort, 21 centers, 9–10 year olds.
• The analysis included 5946 participants (mean age 9.9 years). By date of birth:
  • very premature 28–31 weeks – 55 children;
  • moderately preterm 32–33 weeks — 110;
  • late preterm 34–36 weeks — 454;
  • early term 37–38 weeks - 261;
  • full-term ≥39 weeks - 5066.
• The cognitive battery included the NIH Toolbox (vocabulary, working memory, processing speed, attention, etc.), Rey Auditory Verbal Learning (memorization and retrieval of word lists), and Little Man Task (visual-spatial skills). A composite cognitive score was constructed from the results.
• Genetics were controlled for via a polygenic score for cognitive performance/education; gender, age, socioeconomic status (income, parental education, place of residence), pregnancy characteristics (gestational complications, etc.), and child characteristics were also controlled.

What did they find?

1) Moderate prematurity (32–33 weeks) — consistently lower cognitive results.
On average, the composite cognitive score of such children was lower than that of their full-term peers. The following dropped especially noticeably:

• vocabulary,
• working memory,
• episodic memory (including short-term and long-term recall of a list of words).

The effect remained significant after accounting for genetics, SES, and obstetric factors, suggesting it was not just a matter of heredity or family background.

2) The earlier the baby was born, the more noticeable the difference.
The lowest rates are for babies born at 32 weeks and earlier. At 33 weeks and later, the dip is smoothed out.

3) Late preterm (34–36) and early term (37–38) — no significant differences.
In this sample, their results at 9–10 years are, on average, comparable to full-term.

4) Gender did not matter.
Boys and girls did not differ in the strength of the association between birth date and cognitive outcomes.

5) Genetics are important, but weaker than the gestational threshold.
The polygenic score, as expected, is positively associated with abilities. But the effect of prematurity (for 32–33 weeks) was several times stronger than the average contribution of PGS in this model. This is not “against” genetics, but to the question of whether the biological stress of prematurity is an independent factor.

How to interpret this in simple words

• A few weeks' difference within the third trimester is no small thing. For some babies, being born before 34 weeks means that some of the brain's fine-tuning (especially for language and memory) has been interrupted and has to be caught up later.
• This is not a sentence or a universal scenario. Many children compensate successfully; average differences in a group do not equal individual destinies. But in a population, the risk of downward shift is statistically significant.

Limitations (why you shouldn't make too bold conclusions)

• The study looks at a 9-10 year snapshot rather than following year-by-year trajectories (causal inferences are limited).
• The ABCD project excluded babies born extremely early and with very low birth weight - the results do not extend to the most severe cases.
• Polygenic scores explain only part of the genetic variation in ability; "hidden" genetics and environment also play a role.
• The number of very preterm infants in the sample is small, meaning the statistical power for this group is lower.

What this means for parents, doctors and schools

• Early identification and support: Children born before 34 weeks should be routinely assessed for speech, vocabulary, working memory and verbal recall as early as primary school.
• Targeted interventions work. Speech therapy, memory training, reading aloud, a rich language environment, cognitive games - all this helps to "catch up" with critical domains.
• Quieter, softer, longer. In the first years of life, such children benefit from regimes that reduce stress and overload, and a consistent, uninterrupted pedagogical strategy.
• Teamwork. Not only neonatologists and pediatricians, but also school psychologists, teachers, and speech therapists should be aware of the risks and outwardly “inconspicuous” moderate prematurity.

Where should science go?

The authors call for long-term (longitudinal) follow-up, inclusion of the genetics of preterm birth itself (not just cognitive), and assessment of which specific early interventions best improve language and memory in children born before 34 weeks.

Conclusion

Data from a large US cohort show that moderate prematurity (32–33 weeks) is associated with poorer performance in key cognitive domains at 9–10 years of age – and that this effect is not explained by genetics or social factors. This argues for systematic screening and support for all children born before 34 weeks, even if they appear “perfectly normal” in the first years of life.