NO do not stop cold turkey! Doctors will usually advise you to wean down, because stopping any addictive substance cold turkey can cause fetal seizures or worse. If you are on a low enough amount (And I can't recommend what amount would be safe you need to ask your doctor) it should be safe to stop, but if you are a heavy smoker you do not want to stop abruptly...this causes trauma to the systems in your body and affects the baby.
Call your OB today, tell them how much you smoke, and ask if it's safe to stop cold turkey. If it's not, ask them to recommend how to cut back and quit, or ask them to recommend a smoking cessation method to help you (the patch, the gum, etc)...and see if there are any smoking cessation programs in your state that you can call for information as well.
yes its safe and the sooner the better for baby