I think the soul is binded to the fertilized egg at conception - but the knowing this life will be miscarried is already understood.
My daughter was stillborn at 6months gestation. I felt her spirit was with me from her conception - that there was a door between my womb and the spirit world...
My understanding in regards to Exit Points is this. When we choose to incarnate into physical form - we take it on as a project (in the spiritual realm) and begin planning.
We ask different soul mates if they are interested in joining/contributing to our life to heal past karma and create...