Explaining premature birth

If your baby is born early - also called 'premature' or 'preterm' - they may need special care.

There are numerous causes of premature birth and the effects, treatment and reasons for prematurity are extensively studied.

Definitions of 'premature' babies

The definition of a 'premature' or 'preterm' baby is one that is born before 37 weeks . There are different categories levels of prematurity and these carry their own risks. 

  • extremely preterm ( less than 28 weeks)
  • very preterm (28 to 32 weeks)
  • moderate to late preterm (32 to 37 weeks).

Generally, the earlier a baby is born the higher the risk is of health problems

Causes of premature birth

We still have a lot to learn about premature birth so it's not always possible to explain the causes and why it happens. There are maternal and baby risk factors for being born early, such as infection, placental problems or genetic problems for example, but in many cases the cause is unknown. This is partly why prevention of premature birth is still in need of extensive research - without knowing the causes, a treatment is difficult. 

In our research section you can also learn more about the research we carry out into preterm birth and its prevention.

Read more


  1. World Health Organisation, Preterm birth fact sheet, Geneva WHO, 2012 (http://www.who.int/mediacentre/factsheets/fs363/en/)
  2. Norman JE, Greer IA (2011) Preterm labour: managing risk in clinical practice,Cambridge University Press 
  3. BAPM (2008) Management of acute in-utero transfers: a framework for practice.London, British Association of Perinatal Medicine
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Last reviewed on October 4th, 2016. Next review date October 4th, 2019.

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