Is it safe to take narcotic pain killers while you're trying to concieve?

My husband and I have been TTC for about 5 months now. Recently, I've been regularly taking the narcotic Vicodin (tylenol with codine) for my back pain. Is this safe? Should I keep taking them now that I've been trying to concieve? Or should I stop once I actually become pregnant? If so, how far along should I be pregnant to stop taking them? Any women experience the same thing? What did you do? Was your baby healthy?