Within pair association between birth weight and blood pressure at age 8 in twins for a cohort study

Objectives To study the association between birth weight and blood pressure in children from multiple pregnancies (multiplets), mostly twins, to deter mine whether maternal or genetic factors are responsible for time associati on. Design Cohort study. Setting Southern Tasmania. Subjects 888 children including 104 multiplets (32 monozygotic, 72 dizygoti c). Main outcome measure Systolic blood pressure (mm Hg). Results Blood pressure decreased with birth weight and increased with curre nt body mass. After adjustment for age and body mass, systolic blood pressu re changed by -1.94 mm Hg (95% confidence interval -2.89 to -0.98) per 1 kg increase in birth weighs of singletons; For multiplets, blood pressure cha nged by -7.0 mm Hg (-10.1 to -3.9) for each 1 kg increase in birth weight T his was little altered in within pair analyses (-5.3, -13.8 to 3.2) and was similar fur both monozygotic (-6.5, -22.5 to 9.4) and dizygotic (-4.9, - 1 5.8 to 6.0) pairs. Conclusion Because the association between birth weight and blood pressure was largely unchanged in within pair analyses, exposures originating in the mother (such as nutritional status) cannot be wholly responsible. The asso ciation also remained within monozygotic pairs, suggesting that genetic pre disposition is not wholly responsible either. The principal causal pathway must concern mechanisms within the fetoplacental unit. The stronger associa tion in multiplets suggests that factors adversely influencing both blood p ressure and birth weight are more prevalent in multiple pregnancies.