Birth weight was standardised for sex and gestational age, giving a birth weight standard deviation score (SDS). The standardisation was based on reference values from Swedish singletons born in 1977-1981 with a gestational age of at least 28 weeks. Hence in this study we focused on mortality from 28 weeks onward. From 28 to 32 weeks of gestation there was hardly any difference in birth weight SDS between twins and singletons. The growth disadvantage of twins became obviously after 32 weeks. The same pattern of difference in birth length SDS was also seen.