Data were entered twice with automatic checks for consistency and range. Analyses were carried out using Stata 9.0. After descriptive analyses, the incidence of fractures was calculated for each sub-group of the independent variables using the chi-square test for heterogeneity of linear trend. Incidence of fractures in each given age was calculated as
the number of new cases divided by the total number of subjects. Multivariable analyses were performed using Logistic and Poisson check details regression, following a hierarchical framework defined a priori, as suggested previously [12]. The distal level included sex, family income and schooling. The intermediate level included maternal BMI, smoking, and age. The proximal level included birth weight, length, and gestational age. The effect of each independent variable on the outcome was adjusted for other covariates in the same level or above in the hierarchical model [12]. In the logistic models,
the lifetime incidence of fractures (yes/no) were used as the outcome variable, while in the Poisson regression, the number of fractures reported (0, 1, 2, 3, 4) was used. The Ethical Committee of the Federal University of Pelotas Medical School approved the study protocol and written informed consents were obtained from parents or guardians. Results Out of the BLZ945 cost 5,249 participants of the cohort, 141 were known to have died before the 2004–2005 follow-up visit. Overall, 4,452 cohort members were located in this visit, resulting in a follow-up rate of 87.5%. Table 1 presents RANTES follow-up rates according to key baseline characteristics. Follow-up rates did not vary according to sex and birth weight, but were slightly higher among adolescents belonging to the poorest families, born to mothers from the intermediate schooling groups, and who were obese. Although statistically significant, these differences in terms of follow-up rates were small. At least 79.9% of the cohort members were traced regardless of the sub-group. Table 1 Follow-up rates at 11 years according to key baseline characteristics
Variable Original cohort (number and %) % located a P value b Sex 0.18 Boys 2,580 (49.2%) 86.9 Girls 2,667 (50.8%) 88.1 Family income (minimum wages) <0.001 ≤1 967 (18.4%) 88.3 1.1–3.0 2,260 (43.1%) 88.7 3.1–6.0 1,204 (22.9%) 88.9 6.1–10.0 433 (8.3%) 79.9 >10.0 385 (7.3%) 82.6 Maternal schooling at birth (years) <0.001 0 134 (2.6%) 82.1 1–4 1,338 (25.5%) 88.7 5–8 2,424 (46.2%) 89.9 ≥9 1,350 (25.7%) 82.5 Birth weight (g) 0.16 <2,500 510 (9.8%) 89.8 2,500–3,499 3,361 (64.2%) 86.9 ≥3,500 1,361 (26.0%) 87.9 Pre-pregnancy body mass index 0.004 <20.0 kg/m2 1,147 (22.5%) 87.6 20.0–24.9 kg/m2 2,811 (55.2%) 86.6 25.0–29.9 kg/m2 894 (17.5%) 90.3 ≥30 kg/m2 245 (4.8%) 92.2 Overall 5,249 (100.0%) 87.