I used to work for an OB/GYN and trust me, they will drug test you without your knowledge or consent and if you test positive, they will ask you to sign a release to leave their practice. At least that is what our doctors did. They will not be responsible for anything that happens to the baby if you are taking any kind of drugs and they cover their ass for their malpractice insurance. We released quite a few patients from our care because of their testing positive for drug use: marijauna and other drugs. They just will not take the risk and be put in a position for you to sue them if something happens to the baby.

So, besides losing your doctor, its just a really bad idea to smoke or drink while you are pregnant. Anything you do affects the baby.
I have a 14 year old with bad sinus and kidney problems and I have always worried that it was the pot smoke and cigerrette smoking for the first 3 months until I found out I was pregnant that caused her to have these problems all her life. She's had 2 surgeries for these problems. I know it may not have been, but it also may have been my actions and I'll never know and always wonder. For your child's sake, give it up, it's only for a few months.