Can a new mother test positive for drugs but not the new born baby?

I would want to know what was tested and when. If I need to find out if the infant was exposed during pregnancy, I test in ways that must be done on the kids first poop or on any hair. After a few days the poop record is gone, hair is still okay and the pee may be clear. There are specific testing methods for differing situations. If you don't look in the right way you may not find anything.