I second DC's not letting your LO find out lol. Darcy did the same to us...though it was much later in the piece (like 36weeks).

We didn't find out with DD, so it was easy enough for us to get away with it with DS. But I found out accidentally at 34weeks. We told people we knew but only one person ever knew with 100% assurance (ie not the daycare teachers from Darcy blabbing), and that was the day he (the person) died.

This time I have been up front telling everyone we aren't finding out. That way even if we do - it's a plausible lie