Many blood vessels in the premature baby’s brain have very thin walls and so are prone to bleed if the baby is sick for any reason or has unstable circulation such as low  blood pressure. The bleeding occurs close to the central fluid system in the brain( the ventricles) and bleeding can extend into the ventricles or into the brain tissue 

• Head ultrasounds are often given to premature babies (especially ELBW and VLBW) usually within the first two weeks after birth to detect IVH
• Many ELBW babies have very small bleeds that do not damage the brain
  • However, some can have a large amount of bleeding
  • If this becomes an issue for your baby, the doctors and/or nurses will discuss with you the size of bleed, and what kind of follow up your baby needs.

Reference:

AbbVie Corporation (Ed.). (2015). Preemie Parent Handbook (4th ed.). Canada: AbbVie Corportation.

Image: Cancer Research UK, CC BY-SA 4.0, via Wikimedia Commons