Low birth weight (LBW) is defined by the World Health Organization (WHO) as a birth weight of less than 2,500g (5lbs 8oz). Low birth weight babies generally fall into two groups: those born before term (37 weeks) and those who are small for their age. Low birth weight babies have a higher chance of infant mortality, morbidity and impaired cognitive development, alongside other health issues, compared with babies of normal birth weight. It can also lead to poorer health in later life, and is associated with coronary heart disease and diabetes in adulthood.
At a population level there are inequalities in low birth weight and a high proportion of low birth weight births could indicate lifestyle issues of the mothers and/or issues with the maternity services.
This indicator is in line with the government's direction for public health on starting well through early intervention and prevention. It has also been included in the Department of Health business plan within the context of addressing issues of premature mortality, avoidable ill-health, and inequalities in health, particularly in relation to child poverty.
There is a strong association between LBW and the deprivation status of the mother. Reducing the number of babies of LBW is therefore important in breaking the inter-generational cycle of health inequality. Other factors which have an impact on LBW are the general health of the mother, smoking status, nutrition, drug or alcohol use during pregnancy, and socio-economic position. The age of the mother is also important, with teenage mothers more likely to have a LBW baby.
The WHO definition of low birth weight mainly serves for comparative health statistics and is not appropriate for clinical care.
For further information around child and maternal health please see the Public Health England profiles.
Page updated July 2017