Low birth weight

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
mother's young age

At a population level, a high proportion of low birth weight babies is primarily related to poorer antental 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.

For more information see the recent International comparisons of health and wellbeing in early childhood report.

How does the UK's proportion of low birth weight babies compare internationally over time?

In 2015, 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 2015, Greece had the highest proportion of low birth weight babies with 9.2% and Finland had the lowest with 4.2%.

Over the past 15 years there has been little change among all OECD countries. The proportion of low birth weight babies in the UK decreased from 7.5% in 2000 to 6.9% in 2015. Greece and Japan have consistently had the highest proportion of low birth weight babies, and Finland and Sweden the lowest.

Updated April 2018.

About this data

Low birth weight: 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. For more details see OECD Health Statistics 2017, Definitions, Sources and Methods.

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