RESULTS Follow-up rates at the 6 months and 1, 4 and 14e15 year follow- up visits of the 1993 Pelotas (Brazil) birth cohort were 96.8%, 93.4%, 87.2%, and 85.6%, respectively. Full datasets were avail- able for 833 adolescents. Subjects included in the analysis were similar to the rest of the cohort: 47.7% versus 49.7% were men and 20.3% versus 20.1% belonged to the poorest wealth quintile at birth. Outcome variables were also similar in the two groups (systolic blood pressure: 119.2 vs 119.4 mm Hg; BMI: 21.3 vs 21.5 kg/m2). Table 1 describes the sample in terms of covariates, infancy and childhood weight and length/height gain and adolescent outcomes. Growth faltering was uncommon in the population under study. At the age of 4 years, 2.4% (according to WAZ) or 0.4% (according to BAZ) were underweight and 5.2% stunted (according to HAZ) compared to the WHO Child Growth Standards (below e2 SD relative to the median).19 Descriptive statistics on infancy, childhood and adolescent Maternal, child and adolescent health a precision of 1 mm. Portable weighing scales were used to measure weight at home visits (PLENNA, São Paulo, Brazil). Length was measured at 6 and 12 months with the infantometer used for the birth measures and standing height was measured at 48 months. Measurements were converted into z-scores of weight for age (WAZ), length or height for age (HAZ) and body mass index (BMI; weight/height2) for age (BAZ) using the WHO Growth Standards.19 Outcome variables included systolic blood pressure, BMI, the sum of triceps and subscapular skin folds, and subscapular/ triceps ratios at 14e15 years of age. Blood pressure was measured twice using a wrist digital Omron sphygmomanom- eter and the mean value was used in the analysis. A validation study using mercury sphygmomanometers as the gold standard showed that the quality of the measurements was adequate (mean difference 0.3 mm Hg).20 Participants were measured seated after a 10 min rest. We opted not to treat hypertension as a dichotomous outcome given its low prevalence at this age range. Skin folds were measured three times and the mean value used. The subscapular/triceps skin fold ratio was calculated by dividing the subscapular by the triceps skin fold measure and multiplying this ratio by 100. Interviewers were trained and standardised on weight, height and skin folds measurements within the margins of error of the National Center for Health Statistics.21 Standardisation sessions were repeated every 2 months during ﬁeldwork, which took place from January to July 2008. Confounding variables included child sex, child skin colour, family socioeconomic level (based on an assets index divided into quintiles), adolescent pubertal status (Tanner ’s stages),22 maternal pre-gestational BMI and maternal smoking during pregnancy. We used conditional weight and length/height vari- ables to express the component of weight (or length/height) at a given age that is uncorrelated with earlier measures.14 15 23 Conditional measures express how an individual child deviates from its own previous growth trajectory; thus, expressing acceleration or deceleration in growth. These were calculated as the residuals from linear regressions of weight (or length/height) at a given age on all prior weights (or lengths/heights). For example, a positive residual at 48 months indicates that a child grew more rapidly in the 12e48 month age range than was predicted from his/her weight at birth, 6 and 12 months. Conditional size was expressed in z-scores using the local distribution. The main advantage of this approach is thatdunlike traditional analysesdconditional weight or height at a given age is independent from earlier weights or heights. In describing the results, we used conditional weight at a given age (eg, 12 months) interchangeably with weight gain in the preceding age range (eg, 6e12 months) Nevertheless, all analyses were repeated using the unconditional or crude weight gains, expressed as z-score changes using the WHO standards.19 The analyses were based on four models. First, we report the unadjusted effect of the growth variables on adolescent outcomes. Second, we adjust these analyses for confounding variables measured in infancy and childhood. The third model includes further adjustments for potential mediating varia- blesdadolescent BMI and height. In the last model, conditional weight was adjusted for conditional length/height at the same age and vice versa. Analyses were conducted in Stata version 10.0 and the signiﬁcance level was set at 5% for two-sided tests. All phases of the 1993 Pelotas (Brazil) birth cohort study were approved by the Federal University of Pelotas Ethics Committee. Written informed consent from the parents or caretakers was obtained prior to each wave of data collection. 150 J Epidemiol Community Health 2012;66:149e154. doi:10.1136/jech.2010.124842 Social, demographic and maternal variables N (%) Table 1 variables Sex Boys Girls Skin colour White Black Mixed Others Puberty status (Tanner stages) 2e4 5e7 8e10 Family income at birth (quintiles) 1 (poorest) 2 3 4 5 (richest) Pre-gestational BMI (kg/m2) <18.5 18.5e24.9 25.0e29.9 $30 Smoking during pregnancy No Yes 487 (47.7) 535 (52.3) 631 (61.8) 195 (19.1) 161 (15.8) 34 (3.3) 43 (5.2) 392 (47.0) 398 (47.8) 206 (20.3) 245 (24.2) 189 (18.6) 195 (19.2) 179 (17.7) 97 (9.8) 683 (69.0) 158 (16.0) 52 (5.2) 655 (64.1) 367 (35.9) 95% CI 47.5 to 50.4 49.3 to 55.4 58.8 to 64.8 16.7 to 21.5 13.5 to 18.0 2.2 to 4.4 3.7 to 6.7 43.7 to 50.5 44.4 to 51.2 17.8 to 22.8 21.5 to 26.8 16.2 to 21.0 16.8 to 21.7 15.3 to 20.0 7.9 to 11.7 66.1 to 71.9 13.7 to 18.3 3.9 to 6.6 61.1 to 67.0 33.0 to 38.9 SD 630 1.21 0.62 0.95 1.24 0.84 0.87 SD 3.9 9.8 13.3 26.5 8.6 Infancy and childhood anthropometry Birth weight (g) Weight gain (z-score) 0e6 months Weight gain (z-score) 6e12 months Weight gain (z-score) 12e48 months Length/height gain (z-score) 0e6 months Length/height gain (z-score) 6e12 months Length/height gain (z-score) 12e48 months Adolescent measurements BMI (kg/m2) Systolic blood pressure (mm Hg) Sum of triceps and subscapular skin folds (mm) Subscapular/triceps ratio(102) Height (cm) 1993 Pelotas Birth Cohort, Brazil, 2008. BMI, body mass index. N 1022 1395 1349 1238 1370 1348 1239 N 1022 1022 1022 1022 1022 Mean 2968 0.34 0.35 0.12 0.15 0.07 0.07 Mean 21.3 119.2 25.1 87.0 161.9