What causes a baby at 38 weeks gestation to suddenly have multiple brain hemorrhage

If this has happened to you, I am very sorry. Online there is no way to know what would have caused this case. This is an issue for your doctor to exam and discuss with you, what could have happened.

As Fr_Chuck said, it can be from a number of possible causes that would have to be determined. It could be issues with the baby genetically, problems with the umbilical cord or placenta, health issues of the mother that went undetected or untreated.

I assume that this isn't your child, because doctors would have explained what cause they found.
I'm like you in that I like to know about medical reasons, but sometimes we just have to wait for when the mother wants to talk about it.