I don't know what to do!!

Right from the finding out I am pregnant me and my partner have always just said we wanted to find out if it's a boy or a girl. We find out in 3 weeks, but recently after having a chat with his parents he has now decided he doesn't want to find out. Since his mum said it spoils the surprise!! And as I can not give him a better reason why I want to know except for the fact that I just want to know, he doesn't want us to find out. I told him that they can just tell me and he can leave the room but that isn't good enough as then he feels we won't be in it together. What do I do? I really want to know but I also don't want to take the surprise away from him if that is what he wants. It makes it nicer when buying clothes but he doesn't feel baby clothes should be gender specific (which is kind of true) and if it is a boy we need to think hard about the name (we both already agree on the girl name)