What negative effects can eating/ smoking cannabis have to an unborn child?

Cannabis...: Contains thc. This is, as you undoubtedly know, a mind altering substance. The brain of the fetus is very sensitive developmentally, and substances that effect you can effect him, perhaps permanently. I don't think the full potential effects of thc (and the hundreds of other substances ingested when you smoke/eat marijuana) is fully known, but i sincerely doubt it does any good. So don't.

Small head: There are a variety of studies of cannabis effect with conflicting results.Some report greater frequency of learning disabilities & some don't.Most agree that infant born to users have smaller head size.Good data is hard to come by as many don't share the information readily & their is overlap with other recreational drugs like alcohol and nicotine that obscure results.

Prematurity: Good data demonstrate higher incidence of prematurity, chromosomal breaks or abnormalities, and later learning disabilities in fetuses exposed to marijuana. Much of this data comes from countries were the government maintains robust and unified health information such as scandinavia or new zealand, and therefore has high validity.