Preterm birth, which occurs before 37 completed weeks of pregnancy, is the biggest cause of newborn deaths and the second biggest cause of deaths in children under five.
Preterm babies are at increased risk of illness, disability and death. The World Health Organisation gives the following definitions for the different stages of preterm birth:
- extremely preterm: before 28 weeks
- very preterm: from 28 to 32 weeks
- moderate to late preterm: from 32 to 37 weeks.
Globally, more than 1 in 10 pregnancies will end in preterm birth (and this number is rising). in the UK, around 80,000 babies are born each year needing specialist hospital care – this is 1 in 9 babies.
In babies born preterm, the chance of survival at less than 23 weeks is close to zero, while at 23 weeks it is 15%, at 24 weeks 55% and at 25 weeks about 80%.
The length of gestation typically reduces with each additional baby. On average, most singleton pregnancies last 39 weeks, twin pregnancies 36 weeks, triplets 32 weeks, quadruplets 30 weeks and quintuplets 29 weeks. Almost 60% of twins are born preterm, while 90% of triplets are preterm.
Premature birth is the biggest global killer of young children, with more than 1 million children dying each year due to the complications of preterm birth, mostly in the developing world.
Causes of preterm birth
- 25% of preterm births are planned because the mother and/or baby are suffering life-threatening complications such as pre-eclampsia, kidney disease or growth restriction.
- 20% are due to waters breaking early (premature rupture of the membranes).
- 25% are due to an emergency event, for example, placental abruption (when the placenta detaches itself from the uterus), infection, eclampsia or prolapsed cord (when the umbilical cord exits the body before the baby).
- In 40% of cases the cause is not known.
Survival rates and long-term outcomes of preterm birth
- In England, survival rates of very premature babies increased from 53% in 2006 to 80% in 2011.
- Survival increases by 9.5% for each week the baby stays in the womb if the baby is born at around 23 weeks, and 16% per week if the baby is born at around 25 weeks.
- A study following the progress of very premature babies (born before 27 weeks) in the UK and Republic of Ireland found a high level of disability once the children reached 6 years of age.
- When children born before 26 weeks were reassessed in middle childhood (aged 11 years), the researchers found that 45% had serious cognitive impairment.
This unique Preterm Surveillance Clinic – funded by Tommy's as part of our research in St Thomas' Hospital, London, has won an NHS Innovation Challenge Prize, for its success in reducing the number of premature births in South East London.
Tommy’s prematurity research centre in London is based at St Thomas’ Hospital. Opened in 1995, it is the first Maternal and Fetal Research Unit in the UK. It houses 87 clinicians, scientists and postgraduate students and last year published 78 scientific papers in peer-reviewed journals.
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 World Health Organization. Preterm birth. 2015. Available at: http://www.who.int/mediacentre/factsheets/fs363/en/ (accessed 2 February 2016).
 Bliss.org.uk. Statistics. Available at: https://www.bliss.org.uk/pages/category/statistics (accessed 2 February 2016).
 Cloherty JP. Care of the extremely low birth weight infant. Manual of neonatal care (7th edn). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2012, p. 146.
 American Pregnancy Association. Complications in a multiples pregnancy. Available at: http://americanpregnancy.org/multiples/complications/ (accessed 19 February 2016).
 National Institute for Health and Care Excellence (NICE). Preterm labour and birth. London: NICE, 2013. Available at: http://www.nice.org.uk/guidance/ng25 (accessed 2 February 2016).
 Henderson C, Macdonald S. Mayes midwifery: a textbook for midwives. Philadelphia: Bailliere Tindall, 2011.
 Salter J. Premature babies: How 24 week-old babies are now able to survive. Daily Telegraph, 17 November 2014.
 Costeloe KL, Hennessy EM, Haider S, et al. Short-term outcomes after extreme preterm birth in England: comparison of two birth cohorts in 1995 and 2006 (the EPICure studies). BMJ 2012;345:e7976.Hide details