How can a mother test positive for benzodiazepines and her new born tested positive for meth and weed, no benzodiazepines. and the mother had no meth ?

Some basics: When you test for drugs in a newborn there are samples you can get that will reveal ANY drug exposure, sometimes as far back as 12 weeks gestation. These exposures do not clear over time but remain a record of exposure. If it finds it, there was exposure. The mother with her active metabolism may discard past evidence of exposures & only reveal drugs within the last week to month.