See, I wouldn't bring it up at all. Not unless I needed to, as in, if something did go wrong. Mentioning stillbirth or the notion that things might turn out that way (to me) would be too confronting to an already vulnerable pregnant woman. Not that stillbirth shouldn't be discussed in society, but I personally wouldn't put it in a contract. In the event of stillbirth, I would personally give them any money they paid me back (not in the sympathy card, but at a later date), or if I hadn't been paid yet, I'd mention it quietly the next time I visited (but again, not in the card or immediately after).