I think that the question of "why would a pregnant woman frivolously and intentionally drink teratogens" is similar to the question of "why would a pregnant woman have a frivolous late-term abortion" or "why would a man expecting a child decide to bankrupt his family spending all his money on saffron". There isn't a lot of it happening.

And yeah, if there was a saffron epidemic among fathers-to-be, it would be worth investigating, because it would be a problem. But I don't think anyone *wants* to ingest teratogens, except in cases like dcltdw mentions, where there are further compelling reasons like medical necessity. (Actually, you do get this sort of thing with cancer - hey, wait, now chemotherapy doesn't cause problems for the fetus? I did not know that! I have derailed myself here.)