Why does ivh mainly happen in premature babies?

Yes: The reason for this is at least two fold. First, their brain blood vessels are fragile and still developing. Second, their brain blood vessels do not regulate blood pressure very well. Thus, fragile premature blood vessels see large fluctuations in blood pressure (particuarly with serious illness) that cause damage and even rupture. After 32 weeks gestation, these problems abate significantly.

Anatomy changes: As fetuses mature, the anatomy of an area in the brain called the germinal matrix changes. That area is rich in blood vessels called capillaries that are susceptible to injury in premature babies, but in term babies this area regresses and becomes less prone to bleeding.

Uterus best incubatr: Premi babies are by definition not ready for the outside world. When they are delivered & staff scrambles to assist their breathing and support a weak blood pressure, shifts in blood flow & blood pressure strain the immature vessels of the brain & they may leak to form an ivh. As the baby "ripens"the vessels strengthen & their need for support also drops.Ivh can happen then but seldom does.