Growth trajectory matters: interpreting the associations among birth weight, concurrent body size, and systolic blood pressure in a cohort study of 378,707 Swedish men.

The interpretation of the inverse association of birth weight with adult blood pressure after adjustment for concurrent size has been debated. In a large sample (n = 378,707) of Swedish men aged 18 years, born between 1973 and 1984, the authors found considerable variation in birth weight within strata of identical adult body mass index (to the nearest kg/m(2); range: 17-33 kg/m(2)), weight (nearest kg; range: 52-100 kg), and height (nearest cm; range: 164-196 cm). The regression coefficient of systolic blood pressure on birth weight was inverse and the same within strata of identical body mass index (p(interaction) = 0.80), weight (p = 0.79), and height (p = 0.35). When the analyses were restricted to those who were born between 39 and 41 weeks' gestation, consistent inverse associations remained within strata of identical adult size. Findings were similar when hypertension (rather than mean systolic blood pressure) was the outcome. These findings demonstrate that, for male babies who grow to be the same size at age 18 years, those who were of lower birth weight have on average higher blood pressure and a greater risk of hypertension. They suggest that growth between conception and early adulthood has relevance to understanding the etiology and, hence, prevention of high blood pressure.