drug tests in preg

I am new to this list but it was reccommended that I ask for the collective opinion here.
Is there anyone who is practicing as a CNM or in AP/IP care that routinely does a rapid drug screen either during an office visit or on admission to the unit in labor? I live in a very rural state and we have had a massive jump in meth and crack use here. I feel like we are missing a lot of the problems (and we have an increase in unexplained TTN and sick babies), but the OBs I work with are not quite sure how to approach the problem.
Does anyone have a protocol that they use that they would be willing to share?
I already have included in our new OB packet that the pateint may be tested at anytime during the pregnancy for drug use. So far no one has even mentioned it.
We have had several poitive screens that were done for cause(pt's behavior, family member reporting use, or other reasons.) The ones that were positive for multiple drugs were not patients I would have expected.
I think I am doing a disservice to the babies by not checking at least once during the pregnancy to see if there is even a problem. I am just not sure how to set up the protocol. If someone has one that works I would greatly appreciate it.
Our referral center states they test all moms in labor,but I can't get a written policy from them.
If there is not a policy available, would anyone like to help me research and wrote one?
Vicki