Many all bad. There is documented increased rate of prematurity, learning problems, adhd, microcephaly. Suspected increase in chromosomal problems. Anyone who would use drugs, legal or otherwise, during pregnancy is irresponsible and cares nothing for their unborn baby. If you plan to conceive, plan to stop all drugs, alcohol and tobacco before you try.
Unknown. Because one cannot do trials on newborn we may never know but if you extrapolate data from adolescents and the cognitive damage and changes in the brain one can only surmise it would affect newborn even more since their brain is still developing.
Not sure.. We're really not sure. But, it is certainly much more likely that smoking marijuana while pregnant would cause more harm than actually help anything. Therefore, if it's not better for the baby and likely harmful, why take a chance? If something were to go wrong with your pregnancy or the baby, why take the chance of living your life wondering if something you did caused it. Just don't do it!