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

Abstract Objectives: To study the association between birth weight and blood pressure in children from multiple pregnancies (multiplets), mostly twins, to determine whether maternal or genetic factors are responsible for the association. Design: Cohort study. Setting: Southern Tasmania. Subjects: 888 children including 104 multiplets (32 monozygotic, 72 dizygotic). Main outcome measure: Systolic blood pressure (mm Hg). Results: Blood pressure decreased with birth weight and increased with current body mass. After adjustment for age and body mass, systolic blood pressure changed by −1.94 mm Hg (95% confidence interval −2.89 to −0.98) per 1 kg increase in birth weight of singletons. For multiplets, blood pressure changed by −7.0 mm Hg (−10.1 to −3.9) for each 1 kg increase in birth weight. This was little altered in within pair analyses (−5.3, −13.8 to 3.2) and was similar for both monozygotic (−6.5, −22.5 to 9.4) and dizygotic (−4.9, −15.8 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 association also remained within monozygotic pairs, suggesting that genetic predisposition is not wholly responsible either. The principal causal pathway must concern mechanisms within the fetoplacental unit. The stronger association in multiplets suggests that factors adversely influencing both blood pressure and birth weight are more prevalent in multiple pregnancies. Key messages Low birthweight is associated with high blood pressure from an early age Maternal factors, including diet during pregnancy, cannot wholly explain the association between fetal development and later risk of cardiovascular disease Because the association between blood pressure and birthweight remained in monozygotic twins, genetic factors are unlikely to be responsible for the association Important causes of the association seem to be operating within the fetoplacental unit during fetal life Further research should now focus on placental function and fetal exposures