Learned that lesson long ago (actually got to learn it at someone else's expense, not my own.)
Certain things you never ask, and that is one of them. I saw one guy eat his words after asking a question about when the baby was due, and he was told the baby was born last week. (Not all ladies emerge from the maternity ward looking like Britney Spears.)
Worse case I saw was when the lady had just lost a child.
In this day of sexual harassment, best topic to engage a lady in would be the weather. Or you can talk to Torre Tames about sports cars.
http://www.eccie.net/showthread.php?t=228867