Smaller-than-expected babies at birth face weaker school results in their teens

Children who are born smaller than expected for their stage of pregnancy tend to perform worse in national school tests years later, with the differences still visible in mathematics and reading scores during the mid-teen years, according to a large new study led by researchers at the University of Warwick. The research, conducted together with the PsychGen Centre at the Norwegian Institute of Public Health and other collaborating institutions in Norway, followed more than 92,000 children from infancy to adolescence and is published in the American Journal of Obstetrics and Gynecology. Its central message is striking: among babies born at full term, it is not simply arriving a few weeks early that matters for long-term academic outcomes, but whether a baby reached an appropriate size for the length of the pregnancy.

The study drew on the Norwegian Mother, Father and Child Cohort Study, known as MoBa, and included 92,551 children who were all born at term, between 37 and 41 weeks of pregnancy. By focusing exclusively on term births, the researchers were able to separate two factors that are often entangled in birth records: the timing of delivery within the term window and the size of the baby relative to that timing. Information collected through MoBa was linked with records from the Medical Birth Registry of Norway and with national education records, allowing the team to trace each child from the delivery ward to the classroom.

Size at birth was assessed in a specific and clinically meaningful way. Children counted as smaller than expected, or small for gestational age, were those who weighed less than most babies of the same sex born at the same stage of pregnancy. This definition matters because it distinguishes babies who are simply small but growing appropriately from those whose weight falls below the expected range for how far the pregnancy had progressed, a pattern that can signal that the intrauterine environment did not fully support the fetus’s growth.

The developmental picture was built from repeated assessments across childhood. Researchers examined the children’s language and motor skills at around six months, 18 months, three years and five years of age. They then analysed results from national school tests in mathematics, reading and English, including tests taken at around 10 to 11, 13 to 14 and 14 to 15 years of age. This longitudinal design, spanning from early infancy into adolescence, is what gives the study its power: rather than a single snapshot, it captures how early differences emerge, whether they persist, and at what point they fade or consolidate.

The headline finding concerns persistence. Children who were smaller than expected at birth tended to achieve lower scores in some school subjects, particularly mathematics and reading, and those differences were still apparent in adolescence. In other words, the association between size at birth and academic performance did not disappear once children entered school or accumulated years of formal teaching; it was still detectable in national test results at 14 to 15 years of age. For a field in which many early-life disadvantages attenuate over time, the durability of this link is notable.

By contrast, the second pattern the team examined told a more reassuring story. When the researchers looked at when within the 37 to 41 week term period babies were born, they found that babies delivered at 37 or 38 weeks tended to have slightly poorer language and movement skills in early childhood than those born at 39 to 41 weeks. Yet those early differences had become minimal by the time the children started school. Being born a week or two before the due date, while still fully term, appeared to carry only a transient developmental cost that was washed out within the first five years of life.

Xuan Zhao, a researcher from the University of Warwick’s Department of Psychology, described the contrast between the two patterns as the most surprising element of the results. According to Zhao, differences linked to being born slightly earlier within the term period largely washed out by age five, while those linked to being smaller than expected were still apparent in school performance at 14 to 15 years of age. The comparison suggests that the two measures, gestational timing and fetal size, are not interchangeable indicators, and that fetal growth restriction may reflect processes with longer-lasting consequences for the developing brain than modest variation in delivery timing among term births.

Professor Dieter Wolke, Professor of Developmental Psychology and Individual Differences at the University of Warwick, offered a possible interpretation of the mechanism. For babies born at term, being small for their stage of pregnancy may indicate adverse effects on the brain that affect learning and last into adolescence, he noted. Crucially, however, Wolke also emphasised that the long-term effects of being born small may be altered by parenting, home stimulation and school support for term-born children. That framing positions the finding not as a deterministic verdict on any child’s future but as a signal about where support can be targeted most effectively.

Professor Siobhan Quenby MBE, from the University of Warwick’s Medical School, highlighted the practical implications for maternity care and for families. Because the study shows that babies who are normal size or large for their stage of pregnancy show no long-term effects of being delivered a few weeks before the due date, she argued that the results should reassure parents whose term babies arrive slightly early. At the same time, she cautioned that not every baby born smaller than expected will experience difficulties, but said the study underlines the importance of monitoring a baby’s growth during pregnancy and ensuring that children receive appropriate support as they develop.

Taken together, the findings carry weight for clinicians, educators and policymakers alike. For obstetric care, they reinforce the value of fetal growth monitoring as a tool that identifies not just immediate perinatal risk but a group of children who may benefit from extended developmental follow-up. For schools and families, they suggest that children born small for gestational age at term represent a population in which early awareness, stimulating home environments and targeted educational support could meaningfully shape trajectories that might otherwise show up as lower mathematics and reading scores years later. With more than 92,000 children tracked from the first months of life to the middle of secondary school, the study provides one of the clearest demonstrations yet that what happens before birth, particularly whether a fetus reaches its expected size, can echo quietly through a child’s academic life well into the teenage years.

Subject of Research: The association between fetal size and gestational age at term birth and neurodevelopmental and academic outcomes from infancy to adolescence

Article Title: Babies who are smaller than expected at birth tend to have poorer school performance as teenagers

Article References: Babies who are smaller than expected at birth tend to have poorer school performance as teenagers. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: birth weight, gestational age, fetal growth, school performance, mathematics scores, reading scores, neurodevelopment, MoBa cohort, Norway, University of Warwick, term birth, adolescence