Introduction Birth weight is a strong predictor of infant mortality, morbidity and later disease risk. Previous work from the 1980s indicated a shift in the UK towards heavier births; this descriptive analysis looks at more recent trends.
Methods Office for National Statistics (ONS) registration data on 17.2 million live, single births from 1986 to 2012 were investigated for temporal trends in mean birth weight, potential years of birth weight change and changes in the proportions of very low (<1500 g), low (<2500 g) and high (≥4000 g) birth weight. Analysis used multiple linear and logistic regression adjusted for maternal age, marital status, area-level deprivation and ethnicity. Additional analyses used the ONS NHS Numbers for Babies data set for 2006–2012, which has information on individual ethnicity and gestational age.
Results Over 27 years there was an increase in birth weight of 43 g (95% CI 42 to 44) in females and 44 g (95% CI 43 to 45) in males, driven by birth weight increases between 1986–1990 and 2007–2012. There was a concurrent decreased risk of having low birth weight but an 8% increased risk in males and 10% increased risk in females of having high birth weight. For 2006–2012 the birth weight increase was greater in preterm as compared with term births.
Conclusions Since 1986 the birth weight distribution of live, single births in England and Wales has shifted towards heavier births, partly explained by increases in maternal age and non-white ethnicity, as well as changes in deprivation levels. Other potential influences include increases in maternal obesity and reductions in smoking prevalence particularly following the introduction of legislation restricting smoking in public places in 2007.
- Qualitative Research
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Contributors REG conceived the study. JDB, REG and AFS carried out the statistical analyses and drafted the initial report. The analyses were interpreted by REG, JDB, ALH and MBT. All coauthors revised the report and approved the final version. REG is the guarantor of this paper.
Funding The work of the UK Small Area Health Statistics Unit is funded by Public Health England as part of the MRC-PHE Centre for Environment & Health, funded also by the UK Medical Research Council.
Competing interests None declared.
Patient consent SAHSU research uses very large routinely collected data sets that are anonymised before being accessed by researchers; therefore, researchers have no sight of identifiable information. We have permission under section 251 of the NHS Act 2006 from the Health Research Authority to acquire these data for which consent would be impractical to collect.
Ethics approval Data use is covered by approval from the Health Research Authority - National Research Ethics Service (HRA-NRES) reference 12/LO/0566 and 12/LO/0567 and by Health Research Authority Confidentiality Advisory Group (HRA-CAG) for Section 251 support (HRA 14/CAG/1039). All data were analysed and stored according to the Statistics and Registration Service Act 2007.
Provenance and peer review Not commissioned; externally peer reviewed.
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