Distributions of birth weights of twins and singletons born at three southeastern Brazilian hospitals were compared after adjustment for gestational age, its quadratic and cubic terms, sex, type of pregnancy, as well as their interactions. The pattern of twin fetal growth rate was retarded in comparison to that of singletons, regardless of the socioeconomic level of the examined population, but the gestational age at which this retardation started seems to be correlated to the income of the mothers. In all cases, after 28 weeks of gestation, female fetal growth was slightly but consistently lower than that of males.
