Social gradient of birthweight in England assessed using the INTERGROWTH-21st gestational age-specific standard

ObjectiveTo determine the socioeconomic gradient of birthweights in England with reference to the prescriptive INTERGROWTH-21st Birthweight Standard.DesignNational cross-sectional study using data from Hospital Episode Statistics.SettingNational Health Service in England.ParticipantsAll singleton babies, live born between 34 weeks’ gestation and 42 weeks’ gestation, between 1 April 2011 and 31 March 2012.Main outcome measuresBirthweight distribution of babies with a birthweight of <10th centile or >90th centile, that is, small for gestational age (SGA) or large for gestational age (LGA) using Index of Multiple Deprivation quintiles as a proxy for socioeconomic status.ResultsOf 508 230 babies born alive between 1 April 2011 and 31 March 2012, 38 838 (7.6%) were SGA and 81 026 (15.9%) were LGA. Median birthweight was 3405 g, median z-score was 0.25 (SD 1.06). Birthweight z-score demonstrated a social gradient, from 0.26 (SD 1.1) in the most deprived areas to 0.53 (1.0) in the least deprived. Women in the most deprived areas were twice as likely to have SGA babies using the INTERGROWTH-21st chart (OR 1.94; 95% CI 1.87 to 2.01) compared with those in the least deprived areas. If all women had the same rate of SGA equivalent to those living in the least deprived areas, approximately 12 410 (30%) fewer babies would be born SGA in England each year.ConclusionsThis study gives a measure of the social gradient in singleton SGA and LGA babies across England using an international standard of newborn size at birth.