In nearly half of premature births, the cause is unknown. We are finding out what we can about the cause and we know some things right now.

One of the few, and most important, identifiable causes of prematurity is drug abuse, particularly cocaine, by the mother.

• Infections. Some studies have found that the body desires to fight infections and perceives the pregnancy as an infection. Also other infections in the body may cause pregnancy complications, even infections in the mouth may trigger the early labor.
• Maternal or fetal stress. Stress on the fetus, such as insufficient bloodflow to the placenta, can cause an early birth.
• Bleeding. If there are any complication in which bleeding occurs, items in the blood may cause uterine contractions.
• Stretching. Multiple births are a leading cause of prematurity due to the stretching of the placenta by multiple children.