Effect of Drug and Alcohol Use in Pregnancy Fetal Development
I think it is pretty safe to say that if it was a one-time occurrence during pregnancy, your fetal development was not harmed by this alcohol or marijuana use.
Marijuana has been shown in studies to have effects on fetal brain development in fetuses that show up later in the child's life. Exposure to marijuana may harm your child's ability to solve problems or concentrate. Plus, there is the mystery factor in any street drug: What else is in there? It is not uncommon for marijuana to be laced with PCP, crack or other drugs. Continued exposure, of course, maximizes all of these risks.
It is imperative that you stop drinking alcohol at this point, as well. There is actually more medical proof that alcohol use is extremely dangerous to pregnancy fetal develoment. This is especially true of fetal development in early in pregnancy.
One night of partying isn't likely to harm your baby, but continued partying will. I would encourage you to be honest with your doctor, as well, when she asks about drinking or drug use. Even if it was just the one time.
If you have any problems stopping, it is important to ask for help. There are free, anonymous 12-step and other recovery meetings available in almost every town. There are online meetings available, as well, and support groups both online and in real life.
If this was just a one-time or occasional thing for you, then tell your doc, don't indulge again and enjoy the rest of your pregnancy!