I think taht finding an alternative method like hamster said, or a location away from your wife and coming soon child would be best.

If the ultimatum is just for you to keep the smoke away from her and the child it's not unreasonable, and I would work with her on it. alternatively, if she wants you to quit permanently regardless of where or how you do it, I don't think she's being reasonable at all considering she knew about your consumption of drugs before she married you.

I would find out which case it is, and work out something to protect your wife and child from the second hand smoke though, regardless