Yes there have been.

However, like most drugs whether illegal or by prescription, there isn't extensive testing on the effects of THC on unborn babies. No one really wants to risk testing whether the parents or researchers.

There are a couple though. I know one of the more well known studies was on some pregnant mothers from Jamaica and they might have even been Rastas if I remember correctly. I'm sure you can find it.

Another if I remember correctly, there were no noted changes from the group that smoked during pregnancy and the group that didn't. But there is a big BUT coming.

I know this isn't going to be popular with many people here but whenever evaluating you need to look at the design of the study. The size of the groups was very small, like 13 and 25. You can't conduct a proper study with such a small sample size. I don't know how long they tracked the infants in the study either. You need a study with a sample group in the thousands first of all.

So to me the effects of smoking during pregnancy are still undetermined. Infer want you want form the data but for me it is incomplete and needs further study before one can say with a high degree of certainty that marijuana use during pregnancy is safe.