Ignore the idiots on this thread posting these answers, they obviously have no clue what they are talking about, and just want to leave biased opinions just "cause".
There is NO FEDERAL law regarding this issue, so every state has their own laws. Now in Alabama I can not be 100% sure, but there have been instances in the news of women being arrested for child abuse for testing positive at birth. This is a violation of their rights. You are not allowed to be drug tested without your consent, nor is your baby. If they drug test you without YOUR consent AND report you to the police they are in violation of your 4th Amendment rights according to the Supreme Court which ruled on this matter in Charleston, SC. They CAN however, legally report you to Children's Services.
Now most CPS agencies aren't looking for potheads, pot has been proven many times in other countries not to have any lasting effects on babies when used during pregnancy and in fact has been proven to actually be helpful to the mother. The active ingredients in weed do NOT cross the placenta, the metabolites do, so your baby is not getting "high" when you are, they are just getting the crap that stays in your system, which in turn makes it stay in their system. A ton of people in THIS country will say otherwise, but the funny thing is, who are they to say so? They are so against pot they won't even test out the nonsense they are spewing, and all their facts are based on women's say so/admittance and most of those women were also using other drugs, tobacco, and alcohol while pregnant as well. There has been NO CONTROLLED STUDIES IN AMERICA ON THIS ISSUE.
Your best bet, is to deal with the pain as best you can, I also agree I'd much rather toke a few puffs than pop some advil while pregnant, but due to our government we can't so just don't smoke again. Drink lots of water, and stay healthy overall. You have 6 weeks or more to get clean if you don't smoke again, and the amount you smoked is so small you will most likely test negative in less than a week. Don't stress over what you can't change now, just make your next few weeks as easy and worry free as possible. If you only smoked that one time the whole time you will be fine and so will the baby. There are women who do much worse in pregnancy and their kids are all screwed up or disabled because of it and they get to keep their kids. If you do have to deal with CPS just lookup this site called fightcps.com for more info on how to deal with them.
I am glad I live in a state where they stay out of these matters. In NYC a fetus is not considered a person until it is born. If they arrested women for doing drugs while pregnant they'd have to do it to women who drink, women who get abortions, etc. (That's the states stance on the issue not my own but I do agree with their fairness for all) Women who test positive at birth have a chance to get clean before their children are removed, but ONLY if drugs are the only issue. -You don't have stuff for the baby, dirty house, no job, etc AND doing drugs they will take away the baby. CPS knows there are good parents out there who do stuff from time to time and are capable parents and there are parents who do NO drugs and are shitty *** parents.