What if you take prenatal vitamins and smoke marijuanna?

Then you're trying to counter a big bad with a small good. Smoking ANYTHING is bad news for the baby, and you're really giving your baby a poorer start in life - and that only for your own pleasure. If you can't do the responsible thing not even only during the pregnancy - then why on earth do you believe you'll be able to cope with all the other years of parenthood until your kid is old enough to manage by itself?