Subtlety is the key

They say the best way to deliver a news that could possibly upset or surprise someone, is not to make a big deal out of it. What you can do is try to ease it in to a normal conversation.
Say for example:
15 year old girl to mom: "it's a fine weather isn't it? Oh, by the way, mom, i'm expecting to deliver a child in a few months time... Have you seen my earrings? I'm pretty sure I left it here somewhere..."

If the girl's lucky enough (or if her mom is just plain dumb), she and her mom will be too busy looking for earrings to even talk about having a bastard child (or having a good weather).

So what am I trying to say? No, i'm not pregnant (and I also don't wear earrings)!

Well... it wouldn’t be so subtle if I say it now, right? Hehehe…