Ethical dilemma about finding out gender

Had an ultrasound today and my mom came along. I had intended for the tech to write down the sex so I could tell my husband because he’s very scared he’s going to be disappointed at the delivery if it’s another boy. He’s an eternal optimist and is so very hopeful it’s a girl it’ll probably be a big blow if it’s a boy since this is our last baby. Personally I don’t care what baby’s sex is and I’m hoping to wait until delivery. It’s not a big deal for me if my husband knows though, we’ve talked about it a lot and we have already set rules for what he’s allowed to say if something related to the gender comes up.

But anyway tech didn’t write it down, she told my mom outside the room so when I give the go-ahead she’ll tell my husband when I’m not around.

My question: would it be wrong to ask my mom to tell him it’s a boy either way? (Of course only if she’s ok with it)

My thinking is that way if it is indeed a boy he gets these few weeks (I’m 32 weeks) to work through his gender disappointment and find peace with having another son. And if it’s a girl then he’ll be just as genuinely surprised as me at the delivery. I don’t think he’d be offended we lied if he gets to experience the genuine surprise of a girl. Plus if he slips up then I’ll still not really know.

Sorry this is long. I really want my husband to have time to grieve and work through his disappointment so he can be excited if it’s a boy, and he wants that too, but at the same time I really want to share in his joy if it’s a girl.