I wouldn't use it because I didn't like it.
I was reading about cannabis and breastfeeding the other day and it said that THC can be detected in the babies urine 3 weeks after they were exposed to it in breastmilk. They are not capable of breaking it down like adults are. That can't be good in my opinion, and I would imagine that it is just as bad for an unborn baby. I am talking regular use, of course.
Opiates do cross the placenta and are addictive if taken regularly, but do not cause pathological changes. In other words you won't get cancer or other cellular damage from pethadine, morphine or even heroin. So technically they are safe for the baby as long as taken in controlled amounts.

I certainly am not condemning anyone who smokes, it seems like most of us on here have at some point. I do however feel that pot can be much more damaging than we ever give it credit for and its use should not be taken lightly.
Personally I would say eating is worse as you don't know quite how much you have taken for some time after having taken it so it is easy to take too much. Smoking is worse as far as cancer etc, but that isn't really an issue if you are just having it for labour. Just don't spin it if you don't want tobacco.

Almost all illegal drugs were originally intended for something positive for mankind, they have just been abused and given a bad name. Doing anything in small amounts near the end of a pregnancy is unlikely to cause any long term problems, so I guess it is up to the individual.

I've never tried it cos it scares me. Only had pot, mushies and an E.
LOL missymoo. Maybe LSD use was just less prevalent during your teen years?