Birth weight, infant growth, and adolescent blood pressure using twin status as an instrumental variable in a Chinese birth cohort: "Children of 1997"

Purpose: To evaluate the credibility of twin status as an instrumental variable for birth weight and infant growth and to obtain less-confounded estimates of the associations of birth weight or infant growth with adolescent blood pressure (BP). Methods: Prospective population-based "Children of 1997" birth cohort of all surviving infants born in Hong Kong, China, from April to May 1997 with sex-, age-, and height-specific BP z-score at approximately 11years (n=6276) and approximately 13years (n=5305). Results: In instrumental variable analyses, birth weight-for-gestational age z-score was not associated with z-score for systolic BP (0.01; 95% confidence interval [CI],-0.22 to 0.25) or diastolic BP (0.04; 95% CI,-0.09 to 0.18) at approximately 11years adjusted for maternal age and migrant status (F=38.6). Change in weight z-score at 0 to 12months was not associated with z-score for systolic BP (-0.003; 95% CI,-0.15 to 0.15) or diastolic BP (-0.02; 95% CI,-0.10 to 0.07) at approximately 11years (F=54.4). Estimates were similar for BP at approximately 13years, although the F-statistic was lower. Conclusions: Birth weight and infant growth may make little contribution to adolescent BP. Extending consideration of the effects of early life to other growth periods, such as puberty, on BP might yield public health benefits.