SuperImposition By Translation And Rotation Research Articles

Growth curves and the international standard: How children's growth reflects challenging conditions in rural Timor-Leste.

Population-specific growth references are important in understanding local growth variation, especially in developing countries where child growth is poor and the need for effective health interventions is high. In this article, we use mixed longitudinal data to calculate the first growth curves for rural East Timorese children to identify where, during development, deviation from the international standards occurs. Over an eight-year period, 1,245 children from two ecologically distinct rural areas of Timor-Leste were measured a total of 4,904 times. We compared growth to the World Health Organization (WHO) standards using z-scores, and modeled height and weight velocity using the SuperImposition by Translation And Rotation (SITAR) method. Using the Generalized Additive Model for Location, Scale and Shape (GAMLSS) method, we created the first growth curves for rural Timorese children for height, weight and body mass index (BMI). Relative to the WHO standards, children show early-life growth faltering, and stunting throughout childhood and adolescence. The median height and weight for this population tracks below the WHO fifth centile. Males have poorer growth than females in both z-BMI (p=.001) and z-height-for-age (p=.018) and, unlike females, continue to grow into adulthood. This is the most comprehensive investigation to date of rural Timorese children's growth, and the growth curves created may potentially be used to identify future secular trends in growth as the country develops. We show significant deviation from the international standard that becomes most pronounced at adolescence, similar to the growth of other Asian populations. Males and females show different growth responses to challenging conditions in this population.

Fifty years of child height and weight in Japan and South Korea: Contrasting secular trend patterns analyzed by SITAR.

Objectives Japanese and South Koreans have traditionally been shorter than Europeans, but have recently become appreciably taller. The aim was to quantify the secular trend patterns in height and weight growth in the two countries over 50 years using the SITAR growth curve model. Methods Data on mean height and weight by sex in 1‐year age groups from 1 to 20 years were obtained by decade in South Korea (1965–2005) and Japan (1950–2010). The data were analyzed using SITAR (SuperImposition by Translation And Rotation), which estimates a mean curve and three adjustments–size, timing and intensity–reflecting how the individual surveys differ from the mean. A sensitivity analysis compared results for the Japanese data based on cohort as well as period. Results Growth patterns in the two countries changed dramatically over the study period, affecting not only height and weight but also developmental age, in that the growth period advanced in timing and shrank in duration. SITAR fitted the data well. The trends were larger in South Korea than Japan, and puberty timing in Japan stabilized by 1970. Most of the height increment seen in adults had already accrued by age 1.5 years, whereas the adult weight increment accrued throughout childhood. Conclusions The secular height trend in these countries represents increased growth in the long bones during infancy, so it can be viewed as the inverse of stunting. There are striking country differences in growth pattern, but they are not easily explained by differences in national income, diet or lifestyle.

Association Between Linear Growth and Bone Accrual in a Diverse Cohort of Children and Adolescents

Prevention of osteoporosis in adulthood begins with optimizing bone health in early life. The longitudinal association between growth and bone accretion during childhood is not fully understood. To assess the acquisition of whole-body (WB) and skeletal site-specific bone mineral content (BMC) relative to linear growth in a healthy, diverse, longitudinal cohort of children, adolescents, and young adults and to test for differences related to sex and African American race. This investigation was a mixed longitudinal study with annual assessments for up to 7 years at 5 US clinical centers. Participants were healthy children, adolescents, and young adults. The study dates were July 2002 through March 2010. The dates of the analysis were June through December 2016. Anthropometrics, BMC, and body composition via dual-energy x-ray absorptiometry. The superimposition by translation and rotation (SITAR) analysis method was used to define the mean trajectories for height, WB lean soft tissue, appendicular lean soft tissue, and WB and skeletal site-specific BMC acquisition and to measure the age and magnitude of peak velocity for each parameter. The SITAR modeling was performed separately by sex and self-reported race. Among 2014 healthy children, adolescents, and young adults (1022 [50.7%] female and 479 [23.8%] African American) aged 5 to 19 years at study entry, the mean age of peak height velocity was 13.1 years (95% CI, 13.0-13.2 years) in African American boys vs 13.4 years (95% CI, 13.3-13.4 years) in non-African American boys (difference, -0.3 years; 95% CI, -0.4 to -0.1 years) and 11.0 years (95% CI, 10.8-11.1 years) in African American girls vs 11.6 years (95% CI, 11.5-11.6 years) in non-African American girls (difference, -0.6 years; 95% CI, -0.7 to -0.5 years). Age of peak acquisition of WB BMC was 14.0 years (95% CI, 13.8-14.1 years) in African American boys vs 14.0 years (95% CI, 13.9-14.1 years) in non-African American boys (difference, -0.0 years; 95% CI, -0.2 to 0.2 years) and 12.1 years (95% CI, 12.0-12.3 years) in African American girls vs 12.4 years (95% CI, 12.3-12.5 years) in non-African American girls (difference, -0.3 years; 95% CI, -0.4 to -0.1 years). At age 7 years, children had acquired 69.5% to 74.5% of maximal observed height but only 29.6% to 38.1% of maximal observed WB BMC. Adolescents gained 32.7% to 35.8% of maximal observed WB BMC during the 2 years before and 2 years after peak height velocity. Another 6.9% to 10.7% of maximal observed WB BMC occurred after linear growth had ceased. In the group at highest risk for fracture, non-African American boys, peak fracture incidence occurred approximately 1 year before peak height velocity. In this longitudinal study, height gains substantially outpaced gains in BMC during childhood, which could contribute to fracture risk. A significant proportion of bone is accrued after adult height is achieved. Therefore, late adolescence represents a potentially underrecognized window of opportunity to optimize bone mass.

Classifying Gestational Weight Gain Trajectories Using the SITAR Growth Model.

Gestational weight gain is often characterized by the total amount of weight gained during pregnancy, however, the pattern of gain may be an important determinant of health outcomes. The SITAR (Super Imposition by Translation And Rotation) model has been used to describe childhood growth trajectories and has appeal because of the biological interpretability of its parameters. The objective of this study was to determine the feasibility of applying this model to gestational weight gain trajectories. The study cohort included 3470 normal-weight, overweight, and obese women delivering at Magee-Womens Hospital in Pittsburgh, Pennsylvania, 1998 to 2010. We applied the SITAR model, a non-linear mixed effects model, to serial prenatal weight gain measurements in each pre-pregnancy body mass index (BMI) category. We fit models of varying complexity, and chose the best-fitting model to describe the pattern of weight gain (by its absolute amount, timing, and acceleration) for each BMI group. The most complex SITAR models failed to converge, but reduced models could successfully be fit by specifying fewer random effects and simplifying the modelling of gestational age. Best-fitting models for each BMI group explained between 95% and 97% of the variation in weight gain trajectories. Peak rates of weight gain were reached between the 20th and 22nd weeks, and were higher for normal and overweight women (0.59 kg/week and 0.57 kg/week, respectively) than obese women (0.46 kg/week). Following some modifications, the SITAR model can be used to characterize pregnancy weight gain patterns.

Growth references for Tsimane forager-horticulturalists of the Bolivian Amazon.

Growth standards and references currently used to assess population and individual health are derived primarily from urban populations, including few individuals from indigenous or subsistence groups. Given environmental and genetic differences, growth may vary in these populations. Thus, there is a need to assess whether international standards are appropriate for all populations, and to produce population specific references if growth differs. Here we present and assess growth references for the Tsimane, an indigenous population of Bolivian forager-horticulturalists. Mixed cross-sectional/longitudinal anthropometrics (9,614 individuals; 30,118 observations; ages 0-29 years) were used to generate centile curves and Lambda-Mu-Sigma (LMS) tables for height-for-age, weight-for-age, body mass index (BMI)-for-age, and weight-for-height (WFH) using Generalized Additive Models for Location Shape and Scale (GAMLSS). Velocity curves were generated using SuperImposition by Translation and Rotation (SITAR). Tsimane ≤5 years were compared to World Health Organization (WHO) standards while those >5 years were compared to WHO school age references. All ages were compared to published references for Shuar forager-horticulturalists of the Ecuadorian Amazon. Tsimane growth differs from WHO values in height and weight, but is similar for BMI and WFH. Tsimane growth is characterized by slow height velocity in childhood and early adolescent peak height velocity at 11.3 and 13.2 years for girls and boys. Tsimane growth patterns are similar to Shuar, suggesting shared features of growth among indigenous South Americans. International references for BMI-for-age and WFH are likely appropriate for Tsimane, but differences in height-for-age and weight-for-age suggest Tsimane specific references may be useful for these measures.

Using Super-Imposition by Translation And Rotation (SITAR) to relate pubertal growth to bone health in later life: the Medical Research Council (MRC) National Survey of Health and Development.

Background: To explore associations between pubertal growth and later bone health in a cohort with infrequent measurements, using another cohort with more frequent measurements to support the modelling, data from the Medical Research Council (MRC) National Survey of Health and Development (2–26 years, 4901/30 004 subjects/measurements) and the Avon Longitudinal Study of Parents And Children (ALSPAC) (5–20 years) (10 896/74 120) were related to National Survey of Health and Development (NSHD) bone health outcomes at 60–64 years. Methods: NSHD data were analysed using Super-Imposition by Translation And Rotation (SITAR) growth curve analysis, either alone or jointly with ALSPAC data. Improved estimation of pubertal growth parameters of size, tempo and velocity was assessed by changes in model fit and correlations with contemporary measures of pubertal timing. Bone outcomes of radius [trabecular volumetric bone mineral density (vBMD) and diaphysis cross-sectional area (CSA)] were regressed on the SITAR parameters, adjusted for current body size. Results: The NSHD SITAR parameters were better estimated in conjunction with ALSPAC, i.e. more strongly correlated with pubertal timing. Trabecular vBMD was associated with early height tempo, whereas diaphysis CSA was related to weight size, early tempo and slow velocity, the bone outcomes being around 15% higher for the better vs worse growth pattern. Conclusions: By pooling NSHD and ALSPAC data, SITAR more accurately summarized pubertal growth and weight gain in NSHD, and in turn demonstrated notable associations between pubertal timing and later bone outcomes. These associations give insight into the importance of the pubertal period for future skeletal health and osteoporosis risk.

Association between Prepregnancy Body Mass Index and Gestational Weight Gain with Size, Tempo, and Velocity of Infant Growth: Analysis of the Newborn Epigenetic Study Cohort.

The first 1000 days of life is a critical period of infant growth that has been linked to future adult health. Understanding prenatal factors that contribute to variation in growth during this period could inform successful prevention strategies. Prenatal and maternal characteristics, including prepregnancy obesity and gestational weight gain were evaluated in relation to weight growth trajectories during the first 24 months of life using the SuperImposition by Translation and Rotation (SITAR) method, which provides estimates of infant size, timing to peak velocity, and growth velocity. The study sample included 704 mother-infant dyads from a multiethnic prebirth cohort from the Southeastern United States. The total number of weight measures was 8670 (median number per child = 14). Several prenatal and maternal characteristics were linked with infant growth parameters. The primary findings show that compared to women with a prepregnancy BMI between 18 and 24.9, women with a prepregnancy BMI ≥40 had infants that were 8% larger during the first 24 months, a delayed tempo of around 9 days, and a slower velocity. Mothers who had greater than adequate gestational weight gain had infants that were 5% larger even after controlling for prepregnancy BMI and several other covariates. The findings contribute new data on the associations between gestational weight gain and aspects of early growth using the SITAR method, and support a growing consensus in the literature that both prepregnancy BMI and gestational weight gain relate independently to risk for greater postnatal weight growth.

Childhood Obesity Risk and Prevention: Shining a Lens on the First 1000 Days.

[Author Affiliation]Elsie M. Taveras. 1 Division of General Academic Pediatrics, Department of Pediatrics, Massachusetts General Hospital for Children and Harvard Medical School, Boston, MA. 2 Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, MA.Address correspondence to: Elsie M. Taveras, MD, MPH, Chief, Division of General Academic Pediatrics, Department of Pediatrics, Massachusetts General Hospital for Children, 125 Nashua Street, Suite 860, Boston, MA, 02114, E-mail: elsie.taveras@mgh.harvard.eduThe first 1000 days--the period from conception to age 2 years--is increasingly recognized as an important period for the development, and thus prevention, of obesity and its adverse consequences. In recent years, the National Academies of Sciences, Engineering, and Medicine1 and the NIH2 have convened multidisciplinary workshops to examine the state of the science and promising solutions to reduce the risk of childhood obesity beginning in early life. Additionally, The World Health Organization's Report of the Commission on Ending Childhood Obesity3 emphasized the important role of the preconception, antenatal, and early childhood periods in prevention of childhood obesity, and the Robert Wood Johnson Foundation recently published an issue brief on the impact of the first 1000 days on childhood obesity.4 Yet, substantial knowledge gaps remain in the understanding of etiology and plausible behavioral and biological mechanisms of obesity development in early life, and few interventions have been conducted to demonstrate the extent to which prevention in early life has a beneficial effect on infant growth status and obesity-related behaviors.For this theme issue of Childhood Obesity, we asked investigators from a range of disciplines to submit articles that advanced the science of early life obesity risk factors and prevention. Taken together, the articles in this issue begin to narrow the evidence gaps and present emerging and promising methods and approaches to further inform obesity prevention beginning in early life.Claesson and colleagues,5 Fuemmeler and colleagues,6 and Gregory and colleagues7 examined risk factors and interventions in pregnancy. Fuemmeler and colleagues examined associations of maternal prepregnancy obesity and gestational weight gain with infant weight trajectories in the first 24 months of life using the SuperImposition by Translation and Rotation (SITAR) method, which provides estimates of infant size, timing to peak velocity, and growth velocity. Both prepregnancy obesity and greater-than-adequate gestational weight gain were independently associated with risk for greater early postnatal weight growth. These findings suggest that maternal obesity and excessive gestational weight gain may be targets for interventions to prevent child obesity risk. Yet, in two follow-up studies of infants whose mothers participated in interventions to prevent excessive weight gain during pregnancy, Claesson and colleagues and Gregory and colleagues did not find a protective effect of reduced gestational weight gain on offspring BMI. Neither intervention continued to work with the parent-infant dyad in infancy. Previous observational studies that followed offspring of mothers who were participants in interventions targeting gestational weight gain or gestational diabetes, and in which the interventions ceased after birth, have similarly found no spillover effect on childhood obesity.8,9 The studies by Claesson and Gregory suggest the need for risk-reducing interventions to be continued or maintained in infancy once they have begun in the prenatal period in order to influence child obesity risk.Several of the studies in this issue examine risk factors for greater weight-for-length increases in the first year of life10 and at age 6 years11 and with increasing leptin levels from 6 months to 8 years of age. …

A multivariate Bayesian model for embryonic growth.

Most longitudinal growth curve models evaluate the evolution of each of the anthropometric measurements separately. When applied to a 'reference population', this exercise leads to univariate reference curves against which new individuals can be evaluated. However, growth should be evaluated in totality, that is, by evaluating all body characteristics jointly. Recently, Cole et al. suggested the Superimposition by Translation and Rotation (SITAR) model, which expresses individual growth curves by three subject-specific parameters indicating their deviation from a flexible overall growth curve. This model allows the characterization of normal growth in a flexible though compact manner. In this paper, we generalize the SITAR model in a Bayesian way to multiple dimensions. The multivariate SITAR model allows us to create multivariate reference regions, which is advantageous for prediction. The usefulness of the model is illustrated on longitudinal measurements of embryonic growth obtained in the first semester of pregnancy, collected in the ongoing Rotterdam Predict study. Further, we demonstrate how the model can be used to find determinants of embryonic growth.

The relationship between Insulin-like Growth Factor 1, sex steroids and timing of the pubertal growth spurt.

SummaryObjectiveProgress through puberty involves a complex hormonal cascade, but the individual contributions of hormones, particularly IGF‐1, are unknown. We reanalysed Chard growth study data to explore the tempo of puberty based on changes in both height and hormone levels, using a novel method of growth curve analysis.Design and SubjectsSchoolboys (n = 54) and girls (n = 70) from Chard, Somerset, England, recruited in 1981 at age 8/9 and followed to age 16.MeasurementsEvery 6 months, height and Tanner stages (genitalia, breast, pubic hair) were recorded, and in a subsample (24 boys, 27 girls), blood samples were taken. Serum IGF‐1, testosterone (boys) and oestradiol (girls) were measured by radioimmunoassay. Individual growth curves for each outcome were analysed using variants of the super‐imposition by translation and rotation (SITAR) method, which estimates a mean curve and subject‐specific random effects corresponding to size, and age and magnitude of peak velocity.ResultsThe SITAR models fitted the data well, explaining 99%, 65%, 86% and 47% of variance for height, IGF‐1, testosterone and oestradiol, respectively, and 69–88% for the Tanner stages. During puberty, the variables all increased steeply in value in individuals, the ages at peak velocity for the different variables being highly correlated, particularly for IGF‐1 vs height (r = 0·74 for girls, 0·92 for boys).Conclusions IGF‐1, like height, the sex steroids and Tanner stages, rises steeply in individuals during puberty, with the timings of the rises tightly synchronized within individuals. This suggests that IGF‐1 may play an important role in determining the timing of puberty.

Ethnic and sex differences in skeletal maturation among the Birth to Twenty cohort in South Africa

AimTo examine ethnic and sex differences in the pattern of skeletal maturity from adolescence to adulthood using a novel longitudinal analysis technique (SuperImposition by Translation And Rotation (SITAR)).SettingJohannesburg, South Africa.Participants607...

Velocities of weight, height and fat mass gain during potentially critical periods of growth are decisive for adult body composition.

To examine whether maximal velocities of weight, height and fat mass during potentially critical periods of growth were associated with body composition in young adulthood. Analyses were performed on 277 female and 271 male participants of the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study with anthropometric measurements in young adulthood (18-25 years) as well as early life (0-2 years), mid-childhood (3-8 years) or puberty (9-15 years). Maximum growth velocities were calculated using the SuperImposition by Translation And Rotation (SITAR) routine or polynomial functions and related to adult fat mass index (FMI) and fat-free mass index (FFMI). In early life, faster weight gain was associated with a moderately higher FMI and FFMI in young adulthood in women only (Ptrend=0.01). In mid-childhood and puberty, weight and fat mass velocities were related to adult FMI and FFMI in both sexes (Ptrend⩽0.002): relative differences between the highest and lowest tertiles of these growth velocities ranged 33-69% for adult FMI and 6-12% for adult FFMI. A higher mid-childhood height velocity was related to a modestly higher adult FMI in women only (Ptrend=0.0005). Faster gain in weight and body fat during mid-childhood and puberty appear to be particularly relevant for adult fat mass.

Associations between infant feeding and the size, tempo and velocity of infant weight gain: SITAR analysis of the Gemini twin birth cohort.

Objective:Infant growth trajectories, in terms of size, tempo and velocity, may programme lifelong obesity risk. Timing of breastfeeding cessation and weaning are both implicated in rapid infant growth; we examined the association of both simultaneously with a range of growth parameters.Design:Longitudinal population-based twin birth cohort.Subjects:The Gemini cohort provided data on 4680 UK infants with a median of 10 (interquartile range=8–15) weight measurements between birth and a median of 6.5 months. Age at breastfeeding cessation and weaning were reported by parents at mean age 8.2 months (s.d.=2.2, range=4–20). Growth trajectories were modelled using SuperImposition by Translation And Rotation (SITAR) to generate three descriptors of individual growth relative to the average trajectory: size (grams), tempo (weeks, indicating the timing of the peak growth rate) and velocity (% difference from average, reflecting mean growth rate). Complex-samples general linear models adjusting for family clustering and confounders examined associations between infant feeding and SITAR parameters.Results:Longer breastfeeding (>4 months vs never) was independently associated with lower growth velocity by 6.8% (s.e.=1.3%) and delayed growth tempo by 1.0 (s.e.=0.2 weeks), but not with smaller size. Later weaning (⩾6 months vs <4 months) was independently associated with lower growth velocity by 4.9% (s.e.=1.1%) and smaller size by 102 g (s.e.=25 g).Conclusions:Infants breastfed for longer grew slower for longer after birth (later peak growth rate) but were no different in size, while infants weaned later grew slower overall and were smaller but the timing of peak growth did not differ. Slower trajectories with a delayed peak in growth may have beneficial implications for programming later obesity risk. Replication in cohorts with longer follow-up, alternative confounding structures or randomised controlled trials are required to confirm the long-term effects and directionality, and to rule out residual confounding.

Abstract P085: Infant Weight and Length Trajectories Have Different Impacts on Body Composition at Age 3

Introduction: Rapid infant weight gain has been linked with higher childhood body mass index (BMI) and risk of obesity. However, because BMI cannot distinguish lean from fat mass, the role of infant weight or length trajectories on childhood body composition is unclear. Hypothesis: This study aimed to evaluate how specific aspects of infant growth trajectories are associated with fat mass, lean mass and % body fat at age 3. Methods: Total 323 children age 3 y (46% female, 20% African-American) had body composition measured by dual-energy x-ray absorptiometry, and weight and length measurements from birth to age 2 y from pediatrician growth charts. Growth trajectories were characterized using the SuperImposition by Translation And Rotation (SITAR) model. This technique estimates an average growth curve with random effects that allow individual growth curves to shift up or down (size), shift right or left on the age axis (tempo) or rotate to steepen/flatten the growth curve (velocity). Tempo did not improve model fit so was excluded. Size and velocity parameters for weight and length trajectories were regressed against fat mass (FM), lean mass (LM) and % body fat measurements at age 3. Results: On average, girls had higher FM (3.9 vs. 3.4 kg) and lower LM (8.8 vs. 9.5 kg) than boys. Adjusting for sex, LM at age 3 was significantly higher with greater weight velocity and with longer length size between ages 0-2 (Table), but were not related to length velocity or weight size. Adjusting for sex, higher FM was seen for those with higher weight size between ages 0-2, but was not related to either weight or length velocities. Percent body fat at age 3 was associated with both larger weight size and shorter length size between 0-2 years of age, but not with either growth velocities. Conclusions: Weight and length size and velocity differ in their impact on children’s body composition by age 3. This study suggests that faster early weight gain (higher weight velocity) and longer lengths but not higher overall weight may lead to leaner body composition by age 3.

Prenatal influences on size, velocity and tempo of infant growth: findings from three contemporary cohorts.

BackgroundStudying prenatal influences of early life growth is relevant to life-course epidemiology as some of its features have been linked to the onset of later diseases.MethodsWe studied the association between prenatal maternal characteristics (height, age, parity, education, pre-pregnancy body mass index (BMI), smoking, gestational diabetes and hypertension) and offspring weight trajectories in infancy using SuperImposition by Translation And Rotation (SITAR) models, which parameterize growth in terms of three biologically interpretable parameters: size, velocity and tempo. We used data from three contemporary cohorts based in Portugal (GXXI, n = 738), Italy (NINFEA, n = 2,925), and Chile (GOCS, n = 959).ResultsEstimates were generally consistent across the cohorts for maternal height, age, parity and pre-pregnancy overweight/obesity. Some exposures only affected one growth parameter (e.g. maternal height (per cm): 0.4% increase in size (95% confidence interval (CI):0.3; 0.5)), others were either found to affect size and velocity (e.g. pre-pregnancy underweight vs normal weight: smaller size (−4.9%, 95% CI:−6.5; −3.3), greater velocity (5.9%, 95% CI:1.9;10.0)), or to additionally influence tempo (e.g. pre-pregnancy overweight/obesity vs normal weight: increased size (7.9%, 95% CI:4.9;10.8), delayed tempo (0.26 months, 95% CI:0.11;0.41), decreased velocity (−4.9%, 95% CI: −10.8;0.9)).ConclusionsBy disentangling the growth parameters of size, velocity and tempo, we found that prenatal maternal characteristics, especially maternal smoking, pre-pregnancy overweight and underweight, parity and gestational hypertension, are associated with different aspects of infant weight growth. These results may offer insights into the mechanisms governing infant growth.

Birth weight and longitudinal growth in infants born below 32 weeks’ gestation: a UK population study

ObjectiveTo describe birth weight and postnatal weight gain in a contemporaneous population of babies born <32 weeks’ gestation, using routinely captured electronic clinical data.DesignAnonymised longitudinal weight data from 2006 to...

Early life growth trajectories and future risk for overweight

Objective:Standard approaches have found that rapid growth during the first 2 years of life is a risk factor for overweight in later childhood. Our objective was to test whether growth velocity, independent of concurrent size, was associated with overweight using a nonlinear random-effects model that allows for enhanced specifications and estimations.Methods:Longitudinal data from a birth cohort in Mexico (n=586) were used to estimate growth trajectories over 0–24 months for body mass index (BMI), length and weight using the SuperImposition by Translation and Rotation (SITAR) models. The SITAR models use a nonlinear random-effects model to estimate an average growth curve for BMI, length and weight and each participant's deviation from this curve on three dimensions—size, velocity and timing of peak velocity. We used logistic regression to estimate the association between overweight status at 7–9 years and size, velocity and timing of BMI, length and weight trajectories during 0–24 months. We tested whether any association between velocity and overweight varied by relative size during 0–24 months or birth weight.Results:SITAR models explained the majority of the variance in BMI (73%), height (86%) and weight (85%) between 0–24 months. When analyzed individually, relative BMI/length/weight (size) and BMI/length/weight velocity during 0–24 months were each associated with increased odds of overweight in late childhood. Associations for timing of peak velocity varied by anthropometric measure. However, in the mutually adjusted models, only relative BMI/length/weight (size) remained statistically significant. We found no evidence that any association between velocity and overweight varied by size during 0–24 months or birth weight.Conclusions:After mutual adjustment, size during 0–24 months of life (as opposed to birth size), but not velocity or timing of peak velocity, was most consistently associated with overweight in later childhood.

Early life growth trajectories and future risk for overweight

Using a newly developed statistical technique, our objective was to test whether key aspects of growth trajectories between 0–24 months of age, such as size, velocity, and timing of peak velocity, were independently associated with overweight in late childhood. We used data from a birth cohort in Mexico (n=586) and the SuperImposition by Translation and Rotation (SITAR) method to estimate infant/childhood (0–24 months) growth trajectories for BMI, height, and weight. The SITAR method uses a nonlinear random‐effects model to estimate the average growth curve and each individual's deviation from this average curve on three dimensions—size, velocity, and timing of peak velocity. In separate models for each of the anthropometric measures (BMI, height, and weight), logistic regression estimated the association between overweight in late childhood and size, velocity, and timing of the BMI/height/weight trajectory. In crude models, relative BMI/height/weight (size) and BMI/height/weight velocity during 0–24 months were each associated with increased odds of overweight. In the mutually‐adjusted models, only relative BMI/height/weight (size), but not velocity, remained statistically significant. We found no evidence that the association between velocity and overweight varied by size. These results are not consistent with the hypothesis that growth velocity in infancy programs future risk for overweight.Grant Funding Source : This work was supported by pilot funds from the Berkeley Population Center NICHD R21 (HD056581).

SITAR—a useful instrument for growth curve analysis

Background Growth curve analysis is a statistical issue in life course epidemiology. Height in puberty involves a growth spurt, the timing and intensity of which varies between individuals. Such data can be summarized with individual Preece–Baines (PB) curves, and their five parameters then related to earlier exposures or later outcomes. But it involves fitting many curves.Methods We present an alternative SuperImposition by Translation And Rotation (SITAR) model, a shape invariant model with a single fitted curve. Curves for individuals are matched to the mean curve by shifting their curve up–down (representing differences in mean size) and left–right (for differences in growth tempo), and the age scale is also shrunk or stretched to indicate how fast time passes in the individual (i.e. velocity). These three parameters per individual are estimated as random effects while fitting the curve. The outcome is a mean curve plus triplets of parameters per individual (size, tempo and velocity) that summarize the individual growth patterns. The data are heights for Christ’s Hospital School (CHS) boys aged 9–19 years (N = 3245, n = 129 508), and girls with Turner syndrome (TS) aged 9–18 years from the UK Turner Study (N = 105, n = 1321).Results The SITAR model explained 99% of the variance in both datasets [residual standard deviation (RSD) 6–7 mm], matching the fit of individually-fitted PB curves. In CHS, growth tempo was associated with insulin-like growth factor-1 measured 50 years later (P = 0.01, N = 1009). For the girls with TS randomized to receive oxandrolone from 9 years, velocity was substantially increased compared with placebo (P = 10−8).Conclusions The SITAR growth curve model is a useful epidemiological instrument for the analysis of height in puberty.