how to hide new pregnancy on drinking night?

So my df and I aren't trying for a baby but haven't been careful either. We had unprotected sex on the second third fourth fifth and sixth with no protection and I'm ovulating either yesterday or today, though possibly on the sixth since I had some cramping that felt like ovulation that day too. I never have any problem becoming pregnant, that part is so effortless so I'm almost sure I will be after the last few days. My problem is staying pregnant. So if I am I won't want to tell df for a little while until I think it will stick. I always miscarry around weeks 7 to 8. But we have a regular every other weekend get together with his ex wife and her boyfriend who we are both really good friends with. We always play cards and drink. His ex wife knows I've wanted to get pregnant too, so it will be obvious if I try to get out of it or just don't drink. What should I do to keep it to myself until I'm ready? I don't want to tell df too soon and him be disappointed. And this is the first month I've had to really worry about it too much because we usually are more careful around my.ovulation.