How long does marijuana stay in unborn baby's system?

Variable issue. Since the mom's system will eventually remove the material, the time it takes to clear mom is also shared by baby.It takes 24-57 hrs to remove 1/2 from the body, another 24-57 1/2 the remainder & so on. If anyone is suspicious about exposure they can test the newborns poo & find evidence of cannabis for months after the last exposure.