[Preterm birth: definitions, epidemiology, preventive measures].

Preterm birth is defined as any birth occurring before 37 completed weeks of gestation (WG). It affects 9.9% of live births, representing 13.4 million births a year worldwide. In France, preterm birth rate is of 7.0%. The causes of preterm birth can be grouped into 3 main categories: infectious/inflammatory, vascular, and other. Risk factors, preventive measures, and impact on the child's health depend of these causes. Risks of death and of neonatal complications are strongly associated with gestational age at birth. Other factors are also involved, such as birth weight (fetal growth restriction) or the administration of antenatal corticosteroids. In 2020 in France, survival rates were of 47% for children born alive at 24 WG, 80% at 26 WG, 92% at 28 WG and 97% at 31 WG.