Epidemiology

Worldwide, nearly 1 million babies died due to complications of preterm birth in 2020, with rates stable in recent decades.[3]​ One baby is born premature every 2 seconds and one dies every 40 seconds on average.[3]

In the UK, 7.6% of live births were preterm in 2021; preterm birth rates were highest for black (8.7%) and Asian (8.1%) babies.[4]

In the US, about 1 in 10 babies are born preterm each year.[5][6]​​​​ Preterm birth rates in the US declined 1% in 2022, following an increase of 4% from 2020 to 2021.[5] Between 2020 and 2022, the average percentage of live births that were preterm ranged from 9.2% among Asian/Pacific Islanders to 14.6% among black infants.[6]​ Social disadvantage and genetic polymorphisms may explain some of the observed differences between ethnicities.[7]​​

Preterm birth is attributable to spontaneous and iatrogenic (i.e., for a maternal or fetal indication) causes; one third of all preterm births are iatrogenic.[2]​ Between 1995 and 2004, preterm birth to low-risk European women aged between 20 and 40 years increased by approximately 50%.[8]

Less than 1.5% of all births occur below 32 weeks' gestation.[9]​ Mortality and serious morbidity are uncommon above 32 weeks' gestation, although more subtle long-term effects, such as behavioural problems during childhood, still occur with later gestations.

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