During the first week after birth, some premature infants develop bleeding in the brain (intraventricular hemorrhage), for which there is no known treatment. Brain damage can result.

The more immature the brain is, the more fragile the brain's blood vessels are and the more sensitive they are to changes in blood pressure. So extremely premature infants are at the greatest risk for this problem.

Medicines given to the mom or baby may help reduce the risk of bleeding.