CPS questions...

Hey ladies! I have been seeing frequent posts about cps being called on mothers in labor and delivery for different reasons and it is my worst fear! Under what situations or circumstances is child protective services called? I have never done drugs and or smoked but was prescribed Percocet because of pleural pain in the early third trimester. Should I worry my baby will test positive for opiates? I know technically I shouldn't because I was told to take it by my doctor but all of this talk about false positive drug tests on mom and baby is scaring me!