Marijuana

I know everybody has different opinions on smoking weed while pregnant. Some smoke all the way up until they’re due , and others quit as soon as they find out they’re pregnant. I talked to my doctor about it already , I was 160lbs before I got pregnant & im down to 136 , I’m only able to eat once a day & the nausea is absolutely terrible. She told me if I’m able to eat if I smoke & im able to relax and not feel nauseas on all the time . Than go for it because there’s no proven facts of marijuana causing defects good or bad in the baby. My question is if I do smoke, how early should I stop so it doesn’t show in baby’s system , I’m due December 12th