Any drug infested by mama after week 20 is supposed to show up in baby's meconium. Not all hospitals test
me indium without reasonable cause though. If the drug
use is in your medical record or if your or baby is acting suspiciously, then there will be a test for sure. But I've heard some hospitals tests all meconium. For the safety of your baby, you should be honest with your OB so that you can withdrawal properly at the right time
and all precautions are taken for baby's sake.