Prematurity is a term for the broad category of neonates born at less than 37 weeks' gestation. Preterm birth is the leading cause of neonatal mortality and the most common reason for antenatal hospitalization Babies born before 37 weeks are premature. A premature birth is more likely to happen when a mother has a health problem — like diabetes — or does harmful things during her pregnancy, like smoke or drink. If she lives with a lot of stress, that also can make her baby be born too early