Ronalds G. Study of the relationship between ethnic ancestry and birth weight in babies born to Indian and white parents in England and Wales. Submitted in partial fulfillment of the requirements of the Master of Science degree in Epidemiology, London School of Hygiene & Tropical Medicine, University of London.. 2003.
Background Babies born in the UK to parents from the Indian sub-continent are lighter at birth than white babies. Low birth weight (LBW) is associated with both neonatal and postneonatal morbidity and mortality. Risk factors for LBW are well-established but the causes of the Indian/white difference in the UK remain unclear. Also, studies have been published investigating birth weight in infants born to one white and one Indian parent.
Objectives To compare birth weight in individuals born in the UK in (i) two white parents (‘all-white’), (ii) two Indian parents (‘all-Indian’), (iii) Indian mother and a white father, and (iv) white mother and Indian father (‘mixed ethnicity’).
Design Cross-sectional study using census and routine birth registration data.
Main exposure Ethnic group, classified according to self-defined ethnicity of each parent.
Main outcome Birth weight.
Subjects 125,782 males and females from the ONS Longitudinal Study with Indian or white parents (including 326 with mixed-ethnicity), born since 1975, who had data on birth weight and whose parentage could be confirmed.
Results Ethnic group was strongly associated with birth weight (p<0.001) and was highest in all-white babies, intermediate in the mixed-ethnicity groups and lowest in all-Indian babies. Adjustment for parental socio-economic status, parental age, infant sex and mother’s parity had little effect on the difference between all-white and all-Indian groups, which remained large (360g), or on the relative position of the mixed groups. The small difference between the two mixed groups before adjustment (not significant) was almost totally confounded.
Discussion Results are consistent with previous studies, including unpublished data from Chelsea and Westminster hospital that shows mixed-ethnicity births to be intermediate in weight. Results here suggest that the difference between all-white and all-Indian babies is largely genetically-determined, and do not support a role for a maternal effect beyond that of genetic contribution and maternal environment in adulthood. However, further work is necessary before concluding that there is no difference between mixed groups, beyond chance, and to take into account differences in maternal anthropometry and behaviour between ethnic groups.