A large national cohort study exploring the association between small for gestational age birthweight and educational...

Small for gestational age (SGA) birthweight is an important predictor of childhood intelligence, yet longitudinal evidence on its association with school achievement is scarce. We aimed to explore the association between SGA birthweight and educational achievement in secondary school in a national linked data study of New Zealand adolescents. This population study included children born in New Zealand with gestational age, birthweight and sex information available between 1998 and 2005. This cohort was followed until July 31, 2024. Exclusion criteria were children born overseas, multiple births, and children who moved overseas prior to secondary school examinations. SGA birthweight was defined using the New Zealand Sex-Specific Population Birthweight Standard. Educational achievement was defined as the highest qualification attained in secondary school. The analysis included 372,519 children (n = 25,341 [6.8%] small-for-gestational-age [SGA] and n = 347,178 appropriate-for-gestational-age [AGA]). Compared with infants born AGA, in multivariable analysis, children born SGA were at an elevated risk of achieving no formal school qualification (aRR 1.36, 95% CI: 1.25-1.47) compared to finishing secondary school with the maximum qualification available. This risk was greater for those with severe-SGA birthweight (aRR 1.48, 95% CI: 1.29-1.70). There was a statistically significant interaction with very preterm and preterm birth, indicating that SGA birthweight has a differential association with achievement across gestational ages. Crude estimates were larger, suggesting large contributions from confounders.

Children born SGA had a slightly lower risk of achieving higher secondary school qualifications than their AGA peers. This risk is higher for those not achieving any formal qualification and increases with the severity of SGA. The interaction with preterm birth suggests that the relationship between SGA birthweight and education may differ for very preterm and preterm infants. Adjustment for confounders decreased the associations between SGA birthweight and educational achievement in secondary school, indicating the importance of familial and societal factors.

• Few studies have looked at the association between SGA birthweight and achievement in school. • The relationship between SGA birthweight and achievement remains unclear, as studies seldom adjust for confounding variables.

• This study used administrative data to explore the association between SGA birthweight and educational achievement in secondary school. • There appeared to be a small but statistically significant association between SGA birthweight and education in secondary school. The effect size is small and confounded by social determinants, but the number of children affected is not inconsequential at the population level, with SGA having a prevalence of 10%.