Well it's probably safe, however when one is preggers it is a good idea to lay off smoking and other recreational/medical things that could possible damage your child. I'd say avoid it, simply because of the risk, sure not smoking weed for a while can be unpleasant, but having a child with a disorder that will stay with them for the rest of their life, and knowing that you caused, or having your child taken aways because of a failed drug test, are much worse. Anyway, as a parent you should be putting your child's welfare before your own.