We wanted to wait until the birth to find out too.
I know it's a surprise at any time, but we still felt that for us, it would be a bit of an anti-climax to find out before the birth.
And for me it was. I had a lot of scans because of various problems, and each time I told them that before the scan started. At the 32 week scan I did my "We do NOT want to know" speech and the woman promised she wouldn't even look in that area, there was no need, she was checking other things.
So I was peering excitedly at the screen, safe in the knowledge that she wasn't going to stray south of the belly button, and all of a sudden there it was, this sort of mushroom shape. And I looked at her and she looked at me and I pulled a "don't say a word" face at her and went home with DH and my Mum still chattering about "if it's a boy...if it's a girl" and I knew it was a boy and felt very deflated about the game being given away, even just to me.
It took away my "It's a boy!" moment in the delivery room. Of course, I still had my son so it was still all very exciting, but I felt a bit cheated out of that bit.
And it did make it hard for me to convincingly talk about names and the jokey arguments about "it's a boy! NO! It's a girl!" before the birth.
And when my neighbour was pregnant, they found out at the earliest opportunity, knew it was a boy, named him, talked about him using his name and had everything ready for a boy months before he was born.
So it all felt very flat when they did have him. She said afterwards that she missed all the "what did you have...what have you called him!" excitement from people because she'd already told them months ago. And later she felt she had to keep the name they had chosen before he was born, even though she felt it didn't suit him once she saw him, because people had sent cards and bought presents with the name on it already, including a lot of personalised gifts that were already engraved etc.
It's a bit like peeking at a Christmas present weeks before Christmas morning to me. The present is still special, still just what you wanted, but after you've looked you wish you'd waited because the anticipation of surprise was part of the fun.
People are different, there is no right or wrong, but it will be impossible for your DH to keep the secret, he will tell his family or let something slip to you. So I think in this situation it's best that nobody finds out until the birth.
Can you have a quiet word beforehand and ask them to say the baby is in the wrong position and they can't tell what sex it is? That way, he can't blame you for spoiling his fun (not that he should be if it's upsetting you this much.)