ObjectiveTo evaluate the association between birth weight and birth order in grand grand multiparous women (ie, those who have had at least ten deliveries).MethodsThe longitudinal population consisted of 96 grand grand multiparous women with 1098 singleton deliveries. Two birth cohorts formed the cross-sectional reference populations: one from 1966 with 7564 deliveries and one from 1985–1986 with 5691 deliveries. In each population, birth weight was compared in four birth-order groups: first, second to fifth, sixth to ninth, and tenth to 12th born.ResultsThe birth weight increased with birth order in each population, especially in the longitudinal one. The association remained even after adjusting for gestational age, sex of the newborn, maternal diabetes mellitus, and body mass index. Children born tenth to 12th were 83 g (95% confidence interval [CI] 29, 137) heavier than those born sixth to ninth; these in turn were 29 g (95% CI −27, 85) heavier than children born second to fifth, and those born second to fifth were 169 g (95% CI 54, 283) heavier than first born infants. Further indirect adjustment for the secular trend decreased these contrasts somewhat.ConclusionBirth order is an independent determinant of birth weight even until the tenth delivery.