Infants born before 30 weeks of pregnancy are at highest risk for such bleeding. The smaller and more premature the infant, the higher the risk for IVH. This is because blood vessels in the brain of premature infants are not yet fully developed and are extremely fragile. The blood vessels grow stronger after 30 weeks of pregnancy.
IVH is more common in premature babies who have had respiratory distress syndrome, high blood pressure, and other conditions. The condition may also occur in healthy premature babies who were born without injury. IVH may develop in full-term babies, but this is very uncommon.
IVH is rarely present at birth. If it occurs, it will usually be in the first several days of life. The condition is quite rare after 1 month of age, no matter how early the baby was born.
IVH falls into four groups, called grades. The higher the grade, the more severe the bleeding.
Grades 1 and 2 involve a small amount of bleeding and do not usually cause long-term problems.
Grades 3 and 4 involve more severe bleeding, which presses on or leaks into brain tissue. Blood clots can form and block the flow of cerebrospinal fluid, leading to increased fluid in the brain (hydrocephalus).