Drug Exposure

I hear a LOT of hopeful adoptive parents voice concerns that the child they may adopt might have been exposed to drugs in the womb. In my personal experience, I have never met a birth mother who did drugs while pregnant. But I hear about lots of these situations actually happening, even in domestic infant adoption-not foster adoption. This leaves me wondering how common this actually is? Have you or do you know of anyone else who has adopted a drug exposed infant domestically?