Differences in growth trajectories between white British and Pakistani infants in the UK: analysis of the Born in Bradford birth cohort study

Abstract

BackgroundGrowth during infancy is recognised as being important to future health and wellbeing. Infants born to south Asian mothers are lighter than those born to white mothers; however, information about growth during infancy of south Asians in the UK is largely unknown. We use multilevel linear spline models to describe differences in growth of UK-born white British and Pakistani origin infants from birth to 2 years. MethodsMultilevel linear spline models with knot points at 4 months and 9 months were fitted separately to weight and length data from birth to 2 years from 1434 singleton births (642 white British and 792 Pakistani) from the Born in Bradford prospective birth cohort, born between Aug 24, 2008, and Sept 4, 2009. These models allow for individual variation in growth trajectories and for the change in scale and variance in the measurements over time for all available data from all eligible children under a missing-at-random assumption. We used measurement data from two sources: clinic visits and measurements routinely obtained by health visitors. Four coefficients describe mean birthweight and length and the mean growth in the cohort for the three time periods: birth to 4 months, 4–9 months, and 9–24 months. Sex and ethnic differences in growth trajectories were estimated by fitting interaction terms in the random effects models. Models were further adjusted for maternal smoking, gestational age, and maternal height. FindingsLinear spline multilevel models for weight and length with knot points at 4 months and 9 months fitted the data well; the differences between actual and predicted measurements were small in each period, and individual level residuals were normally distributed. Pakistani boys were on average 0·21 kg lighter (95% CI −0·29 to −0·12) than white British boys, and Pakistani girls were 0·18 kg lighter (–0·26 to −0·10) and 0·5 cm shorter (–0·91 to −0·03) than white British girls at birth. Pakistani boys and girls gained length faster than their white British counterparts between 0 and 4 months (0·3 cm per month [0·1 to 0·5] for boys and 0·4 cm per month [0·2 to 0·6] for girls) and gained more weight per month between 9 and 24 months (0·01 kg per month [0·003 to 0·03] for boys and 0·03 kg per month [0·02 to 0·04] for girls). At age 2 years both ethnic groups had similar weight, but Pakistani boys and girls were longer. Adjustment for maternal smoking, gestational age, and maternal height did not substantially change these differences. InterpretationDifferences exist between the growth trajectories of Pakistani boys and girls and white British boys and girls. Pakistani boys and girls are lighter and shorter at birth than their white British counterparts, but gain weight and length more quickly in infancy. By age 2 years both ethnic groups have similar weight, but Pakistani boys and girls have become taller on average than their white British counterparts. The faster growth in Pakistani children could be beneficial for their early infant or childhood health. However, if the greater rate of weight gain is driven by greater fat gain in this population it could have adverse long-term consequences for their cardiometabolic health and contribute to the increased risk of diabetes and cardiovascular disease in south Asian adults. FundingNational Institute for Health Research (Programme Grants for Applied Research, RP-PG-0407-10044).