mmmmsleep, you sound like a great mate to have at such a difficult time. My DD is almost 17 months and we didn't properly know until she was born, although blood tests came back high. proudmum74 gives great tips there and I agree with her, the health checks take a lot of time and really make you feel how different a time you are having, in comparison to other new parents.
I will love forever the friends who did the usual baby support stuff, turning up with a lasagne ready to eat, buying sweet clothes for her, bringing me Spatone and other post-natal treats. Also those who just got on and asked baby questions, i.e. how much does she sleep and eat etc, so that I could chat about DD as a normal baby rather than explaining everything Down's to them. The most baffling comments for me were about whether 'they' could live independently (i.e. some people with Down's) - DD was a tiny baby and the last thing I wanted to talk about, quite reasonably, was whether she would ever live away from me.
I was given great advice not to waste the first precious days worrying about later life, as its pointless and you'll miss great things. Then also to get one of those crinkly foil survival blankets you get after running a marathon, and let DD lie on it as the sparkles and shines and crackles will really fascinate her, even if she can't move very much. It is such a cheap present but DD lay on it for hours and truly loved it. Good luck, you are a great friend to have.