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The aim of this study was to evaluate the association between size at birth (birthweight and birth length) and height in early adolescence in a prospective birth cohort study in Pelotas, Rio Grande do Sul, Brazil. Interviews were carried out in 1993, including measurements of birthweight and length, and in 2004-2005, including measurements of weight and height. This analysis includes 4,452 individuals, with a mean age of 11.3 years (standard deviation-SD=0.3), representing a follow-up rate of 87.5%. Mean height at 11 years was 145.8 cm (SD=7.9), or 144.9 cm (SD=7.7) in boys and 146.8 cm (SD=7.9) in girls. Birthweight and birth length were positively associated with height in early adolescence in the crude analysis, but after adjustment for confounding and for each other, only the effect of birth length was still significant. A one z-score increase in birth length was associated with a 1.63 cm increase in height at 11 years. The present study shows that birth length is a strong predictor of later height, while the effect of birth weight disappears after adjustment for birth length.

Birth weight has short and long-term effects on health. Some studies have used retrospective data on birth weight, reported by the subject or by the parents. This paper compares data on birth weight measured by the research team in 1993 with birth weight reported by the mother in 2004-2005, using data from the 1993 Pelotas Birth Cohort Study, Rio Grande do Sul State, Brazil. We also evaluate the role of misclassification when exploring the effect of birth weight on a given outcome. Mean difference between the two variables was 20g (SD = 288.3). Agreement for detecting low birth weight was 95.2% in the sample as a whole (kappa = 0.73), but was lower among low-schooling mothers. Mothers of children weighing less than 3,500g at birth tended to overestimate the child's birth weight. Inversely, mothers of heavier children tended to underestimate the values. One out of four mothers reported a difference of at least 200g in birth weight as compared to that measured in 1993. Use of reported birth weight diluted the magnitude of the association with body mass index at 11 years in comparison with measured birth weight. Reported birth weight should be used with great caution, if at all.

Previous studies have suggested that birth size may influence blood pressure in later life. Most of these reported inverse associations only became evident after weight or body mass index at some later age was included in the regression model. In a prospective birth cohort study in Brazil, the effect of birth size on blood pressure at age 11 years was explored. Of the 5,249 cohort members, 4,452 were interviewed. Mean systolic and diastolic blood pressures were 101.9 mmHg (standard deviation, 12.3) and 63.4 mmHg (standard deviation, 9.9), respectively. Birth weight was positively associated with blood pressure in the crude analysis, but this effect was no longer significant after adjustment for confounders. When current body mass index-a possible mediating variable-was added to the model, the association between birth weight and blood pressure tended to become negative, though not quite significant. Birth length showed a positive effect on later blood pressure regardless of the adjustments made. Head circumference, gestational age, and ponderal index were not associated with blood pressure. Children born small for gestational age had lower blood pressure values. The postulated inverse association between birth weight and later blood pressure was not confirmed in this cohort. Instead, a positive effect of birth length was detected.

Background Although there is longstanding evidence of the short-term benefits of promoting rapid growth for young children in low-income settings, more recent studies suggest that early weight gain can also increase the risk of chronic diseases in adults. This paper attempts to separate the effects of early life weight and length/height gains on blood pressure, body mass index (BMI), sum of skin folds and subscapular/triceps skin fold ratio at 14-15 years of age. Methods The sample comprised 833 members of a prospective population-based birth cohort from Brazil. Conditional size (weight or height) analyses were used to express the difference between observed size at a given age and expected size based on a regression, including all previous measures of the same anthropometric index. A positive conditional weight or height indicates growing faster than expected given prior size. Results Conditional weights at all age ranges were positively associated with most outcomes; each z-score of conditional weight at 4 years was associated with an increase of 6.1 mm in the sum of skin folds (95% CI 4.5 to 7.6) in adolescence after adjustment for conditional length/height. Associations of the outcomes with conditional length/height were mostly negative or nonsignificant--each z-score was associated with a reduction of 2.4 mm (95% CI -3.8 to -1.1) in the sum of skin folds after adjustment for conditional weight. No associations were found with the skin fold ratio. Conclusion The promotion of rapid length/height gain without excessive weight gain seems to be beneficial for long-term outcomes, but this requires confirmation from other studies. [ABSTRACT FROM AUTHOR]