Hello, I am so sorry to hear this. First of all, your primary concern should be that the baby will be born sensitized to heroin and will go through withdrawal symptoms, just like the mother. While for an adult withdrawal is very hard, for a newborn they are devastating. Usually doctors recognize a newborn going through heroin withdrawal even before doing tests on them. Your sister can and should stop using right away. Even though at this point in her pregnancy the baby is already sensitized, withdrawal symptoms he will have to go through will be much milder when he is born if the mother stops using now. I hope this helps. Wishing you all the best.