too bald is right, just stop for a couple o' weeks before you do the deed. Better to be on the safe side. Theres no way in the world that your hair is more important than the safety of your kid.
FYI, I stopped taking finasteride for almost a month after 3.5 years and noticed no shedding whatsoever. I started up again without noticing any changes. If you stop two weeks before doin' it, then you should be fine. Don't have to worry about all your hair falling out.