Gestational age at birth and academic performance: population-based cohort study.
Numerous studies suggest pre-term birth is associated with cognitive deficit. However, less is known about cognitive outcomes following post-term birth, or the influence of weight variations within term or post-term populations. We examined associations between gestational age (GA) and school performance, by weight-for-GA, focusing on extremely pre- and post-term births.



Record linkage study of Swedish children born 1973-94 ( n =  2 008 102) with a nested sibling comparison ( n =  439 629). We used restricted cubic regression splines to examine associations between GA and the grade achieved on leaving secondary education, comparing siblings to allow stronger causal inference with regard to associations between GA and school performance.



Grade averages of both pre- and post-term children were below those of full-term counterparts and lower for those born small-for-GA. The adjusted grades of extremely pre-term children (at 24 completed weeks), while improving in later study periods, were lower by 0.43 standard deviations (95% confidence interval 0.38-0.49), corresponding with a 21-point reduction (19 to 24) on a 240-point scale. Reductions for extremely post-term children (at 45 completed weeks) were lesser [-0.15 standard deviation (-0.17 to -0.13) or -8 points (-9 to -7)]. Among matched siblings, we observed weaker residual effects of pre-term and post-term GA on school performance.



There may be independent effects of fetal maturation and fetal growth on school performance. Associations among matched siblings, although attenuated, remained consistent with causal effects of pre- and post-term birth on school performance.
Centre for Women's Mental Health, Manchester Academic Health Sciences Centre, Institute of Brain Behaviour and Mental Health, University of Manchester, Manchester, UK.|Manchester Mental Health & Social Care Trust, Manchester, UK.
Kathryn
K
Abel
Centre for Women's Mental Health, Manchester Academic Health Sciences Centre, Institute of Brain Behaviour and Mental Health, University of Manchester, Manchester, UK.
Hein
H
Heuvelman
Public Health Epidemiology Research Group, Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden.|Centre for Epidemiology and Community Medicine, Stockholm County Council, Stockholm, Sweden.
Susanne
S
Wicks
Centre for Academic Mental Health, School of Social and Community Medicine, University of Bristol, Bristol, UK.|Avon & Wiltshire Mental Health Partnership NHS Trust, Chippenham, UK.
Dheeraj
D
Rai
Centre for Biostatistics, Institute of Population Health, University of Manchester, Manchester, UK.
Richard
R
Emsley
Public Health Epidemiology Research Group, Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden.
Renee
R
Gardner
Public Health Epidemiology Research Group, Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden.|Centre for Epidemiology and Community Medicine, Stockholm County Council, Stockholm, Sweden.
Christina
C
Dalman
D000073978:Academic Performance / Q000706:statistics & numerical data*; D000293:Adolescent; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D008297:Male; D012044:Regression Analysis; D035781:Siblings; D013548:Sweden
Sweden; academic performance; gestational age; post-term; siblings; whole-population cohort