Low birth weight (under 2,500 grams) is associated with an increased risk of infant mortality, developmental problems in childhood and poorer health in later life. A large proportion of babies will be born under 2,500 grams because they are preterm births (born before 37 weeks of pregnancy). Whether they are born prematurely or at full term, the risk of low birth weight is related to:
- smoking while pregnant
- substance and alcohol misuse
- pregnancy health and nutrition
- pregnancy-related complications
- a mother's young age
At a population level, a high proportion of low birth weight babies is primarily related to poorer antenatal maternal health. Differences in rates of premature birth across different countries only account for a small proportion of low birth weight babies. Prioritising policies which target maternal health, both socioeconomic and those relating to antenatal health care quality and access, will contribute to a reduction in the number of low birth weight babies. Reducing the number of babies born under 2,500 grams is an international priority, with the World Health Organisation setting a target in 2012 to achieve a 30% reduction in the number of low birth weight babies by 2025.
For more information, see the recent Understanding the health of babies and expectant mothers explainer.
In 2017, 6.9% of live births in the UK weighed less than 2,500 grams. Compared with the other countries, the UK lies around the middle of the range of values. In 2017, Japan had the highest proportion of low birth weight babies with 9.4% and Finland had the lowest with 4.2%.
Overall, there has been little change among all Organisation for Economic Co-operation and Development (OECD) countries since 2000. The proportion of low birth weight babies in the UK decreased from 7.5% in 2000 to 6.9% in 2018. Greece and Japan have consistently had the highest proportion of low birth weight babies, and Finland and Sweden the lowest.
About this data
The OECD defines low birth weight as the number of live births weighing less than 2,500 grams as a percentage of the total number of live births.
Exact definitions of low birth weight and of live births may differ slightly between countries. Gaps in data series exist because data was not available for these years. For more details, please see Health at a Glance 2019: OECD Indicators.