It's not a thing, it's a baby. Or will be, anyway.
DH really wanted to know with DS1, but I didn't; he said he'd keep it from me but he's absolutely crap at keeping secrets from me, so I refused to let him find out. We compromised in that we always planned to have 2, so I said he could find out with the second one, if we could have a surprise with the first.
When it came to the second one, DH decided not to find out. HIs reasons ranged from slightly strange to totally illogical - I'd had 3 MCs in between, so he didn't want to know because then somehow if I lost it, it wouldn't be so hard to cope with
; also because we hadn't found out the first time and that had worked out ok (we'd had one boy, I'm assuming he meant he'd like a second boy). As it turned out, we did have a second boy, so he was happy (I'm sure he would have been happy if it had been a girl too, btw!)
I think, if you really want to know but your DH doesn't, then you would have a huge commitment on your hands to keep that secret. It would also mean you still couldn't buy things in the "appropriate" gender colour, because it would give it away; you couldn't chat to the baby while he was around in case you give it away; you couldn't chat ABOUT the baby while he was around in case you give it away... you get my drift. It's extremely easy to give it away accidentally and then your DH would be pissed off. But even if you didn't give it away beforehand, you still might when the baby is born - and then your DH would know you'd kept that secret from him the entire time and might still be pissed off.
Are you planning on another? Perhaps use the compromise - he gets his way this time, you get yours the next time. :) And congratulations!