Fetal growth and biological sex are thought to affect behaviour in childhood and adolescence. Fetal growth is often estimated with birthweight, however, birthweight can vary both as a consequence of genetic and environmental factors and furthermore a large literature has suggested that the effects of fetal growth may differ between males and females. We want to test how measured birthweight and birthweight-genetics influence lasting behaviour in males and females and if a mismatch between an individuals potential for birthweight - i.e. their genetically determined birthweight - and their actual birthweight, produces lasting behavioral changes throughout their childhood and adolescence. Finally, we will test if the effects of such a mismatch differs between males and females.