Most preterm babies arrive early without warning. However, some pregnancies are known to be at risk of ending in preterm 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. Tommy's invests more than £400,000 annually into prematurity research.