Reduction of ethnic inequalities in birthweight: a public health paradox

Abstract

BackgroundBirthweight is a key predictor of infant and later adult health. Previous studies have shown substantially lower birthweight in infants of south Asian origin than in those of white European origin. Whether such differences mask increased adiposity in south Asian infants and whether they persist across generations in contemporary UK populations is unclear but important to the development of public health interventions aimed at increasing birthweight. We aimed to compare birthweight, skinfold thickness, and cord leptin between Pakistani and white British infants and to investigate whether the magnitude of any difference varies depending on whether the mother, father, and all four grandparents were born in the UK or south Asia. MethodsWe examined differences in birthweight, subscapular, and triceps skinfold thickness between 4649 Pakistani and 4055 white British infants born at term in the same UK maternity unit and compared cord leptin in a subgroup of 775 Pakistani and 612 white British infants. All infants were born to mothers recruited to the Born in Bradford cohort study between March, 2007, and December, 2010. Around 80% of women invited to take part were recruited to the study and levels of recruitment were broadly similar in both ethnic groups. We investigated whether the magnitude of any differences changed by Pakistani generation and used multiple linear regression models to adjust for a wide range of potential explanatory or masking factors (including smoking, alcohol, maternal glycaemia, body-mass index, height parity, sex, gestation, and socioeconomic factors). FindingsPakistani infants were lighter (adjusted mean difference −234 g, 95% CI −258 to −210) than were white British infants and were smaller in both subscapular and triceps skinfold measurements. The differences for subscapular and triceps skinfold thickness (mean Z score difference −0·27, 95% CI −0·34 to −0·20, and −0·23, 95% CI −0·30 to −0·16, respectively) were smaller than the difference in birthweight (mean Z score difference −0·52, 95% CI −0·58 to −0·47) and attenuated to the null with adjustment for birthweight (0·03, 95% CI −0·03 to 0·09, and −0·01, 95% CI −0·08 to 0·05, respectively). Cord leptin concentration (used as an indicator of fat mass) was similar in Pakistani and white British infants without adjustment for birthweight, but with adjustment became 30% higher (95% CI 17–44) in Pakistani infants than in white British infants. The magnitudes of difference did not differ by generation. InterpretationDespite being substantially lighter, Pakistani infants had similar skinfold thicknesses and greater total fat mass, as indicated by cord leptin, for a given birthweight than did white British infants. Our findings draw attention to a potential problem for WHO guidance and other health policy aimed at increasing birthweight in populations in low-income and middle-income countries and in migrant populations in high-income countries. If mean birthweight increases, but a fat-preserving tendency is maintained, the effect might be simply to increase adiposity, which in turn could worsen long-term cardiometabolic health and increase existing ethnic inequalities in diabetes and coronary heart disease. Policies to reduce ethnic inequalities in birthweight therefore need to consider differences in adiposity, and the possibility that increasing birthweight in south Asian infants might inadvertently worsen health by increasing relative adiposity. FundingJW was funded by a UK Medical Research Council (MRC) Special Training Fellowship in Health of the Public and Health Services Research (MRCGO601712), DAL works in a centre that receives funding from the MRC (G0600705). Cord leptin assays were funded by a British Heart Foundation Project Grant (PG/09/036/27380).