Is it ever appropriate to ask if a woman you know is pregnant?

There’s a young woman at work who looks pregnant. I’m pretty sure, but there’s also the possibility that she’s putting on weight. She’s putting on weight all over rather than just on the belly. She dresses specifically to hide her features now with drapey flowy clothes. She really doesn’t talk to anyone at the office so no one knows for sure.
It’s not like you can ask her because if she’s not you’re really in for it. I guess even if she is pregnant, what business is it of mine?

I’m not asking. I’m going to wait it out.
Would you ask?