Male twins at birth and 18 years later

An 18-year follow-up examination on 56 male twins born in 1962-1963 was done by comparing birth records with the results of medical examinations at drafting for military service in 1981. Of the studied twins, 14.3% were unfit for military service compared with 6.2% of the total population of Norwegian conscripts in the same year. Preterm delivery rather than twinning per se is suggested as an explanation for this result. Vision was impaired in the preterm twins more often than in the total group of conscripts. The general intelligence, measured by standardized tests at the military medical board, did not differ significantly between the group of twins and the control conscripts.