So at what age does a fetus develop a blood Brain Barrier. Is it open before, or closed before?

There is this thing called "Google." You should try it

I've already been there. Very dicey information. If noone wants to help me, I won't be mad.

These interfaces are referred to as “the” blood–brain barrier. It is widely believed that in embryos and newborns, this barrier is immature or “leaky,” rendering the developing brain more vulnerable to drugs or toxins entering the fetal circulation from the mother.Mar 29, 2012https://www.ncbi.nlm.nih.gov › pmcBlood–Brain Barrier - NCBI