Help - how to stop him telling?!

Nooshka • 9/6/15 💙
I am currently 9 weeks pregnant with our first. My partner is dying to tell his 11 year old daughter, since our close family all know already.
BUT we haven't yet had any scans or even heard a heartbeat. We had one meeting with the midwife and she just talked to us and took some blood. Our first scan will be at least three weeks from now but he wants to tell his daughter when we have her this weekend and nothing I say is dissuading him.
What if we tell her and then something is wrong?
Any words of wisdom?