Birth characteristics and different dimensions of intellectual performance in young males: a nationwide population-based study

The study comprised a population-based cohort including all male single births without congenital malformations in Sweden from 1973 to 1976, and conscripted before 1994 (n = 168 068). Information from the Swedish Birth Register was individually linked to the Swedish Conscript Register. The test of intellectual performance included four different dimensions: logical, spatial, theoretical and verbal capacity. These data were available for 80-86% of the males at conscription. Being born small for gestational age (SGA) is associated with increased risk of subnormal capacity in all four dimensions of intellectual performance. In SGA males, short adult stature, or a small head circumference at birth is especially associated with the risk of subnormal logical performance.