A baby born before 37 completed weeks gestation is considered premature. Each year 60,000 babies are born prematurely in the UK and most premature births are spontaneous, with no clear cause. Most of these babies will need urgent neonatal care after birth.
The causes of premature birth are not well understood and for the most part doctors do not know how to prevent it. Babies can be born prematurely for many different reasons, some being:
Pregnancies with twins, triplets or more are more likely to end early.
Pre-eclampsia occurs in about 4% of first-time pregnancies, and can be responsible for premature births.
Stressful and/or traumatic events can start labour early. However, there is no evidence that the normal stresses of day-to-day living can bring on premature birth.
Maternal history of premature birth
Premature rupture of membranes
Genetic factors
Maternal illness
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 31 weeks
Moderate to late preterm: from 32 to 37 weeks.
General UK premature birth statistics
Around 8% of births in the UK are preterm. That is around 60,000 babies each year.
This is higher than many countries in Europe and higher than Cuba and Iran
Of the births that were preterm in the UK:
5% were extremely preterm (before 28 weeks)
11% were very preterm (between 28 and 32 weeks)
85% were moderately preterm (between 32 and 37 weeks).
In 2019, live births where gestational age was under 24 weeks increased to 0.15% compared with 0.13% in 2018 and 0.11% in 2010.
Chances of survival following preterm birth
Medical advances mean that we are getting better at treating preterm babies but the chances of survival still depend on gestational age (week of pregnancy) at time of birth.
Less than 22 weeks is close to zero chance of survival
22 weeks is around 10%
24 weeks is around 60%
27 weeks is around 89%
31 weeks is around 95%
34 weeks is equivalent to a baby born at full term.
Preterm birth and neonatal death
Complications arising from premature birth is the leading cause of neonatal death (death in the first few weeks after birth) in the UK.
Preterm birth and multiple pregnancies
Having more than one baby is a risk factor for preterm birth. On average, most singleton pregnancies last 39 weeks, twin pregnancies 37 weeks and triplets 33 weeks.
Risk of prematurity with singleton pregnancy: 7%
Risk of prematurity with multiple pregnancy: 57%
Risk of disability in preterm children
Generally, the earlier the birth, the higher the risk of problems. However, these are only statistics and cannot predict how an individual child will do; some extremely premature babies do very well and develop into healthy children.
1 in 10 of all premature babies will have a permanent disability such as lung disease, cerebral palsy, blindness or deafness.
1 in 2 of premature babies born before 26 weeks of gestation will have some sort of disability (this includes mild disability such as requiring glasses).
In one study of 241 children born before 26 weeks' gestation the following was found:
22% severe disability (eg cerebral palsy + not walking, low cognitive scores, blindness, profound deafness)
24% moderate disability (eg cerebral palsy + walking, IQ/cognitive scores in the special needs range, lesser degree of visual or hearing impairment)
34% mild disability (defined as low IQ/cognitive score, squint, requiring glasses)
20% no problems.
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