A millennial affectation regarding the impending birth of children.
Color me a traditionalist, but I remember the days in which at the first ultrasound, the technician would quietly ask "do you want to know the gender of your child?" Most people say yes, and they'd simply say "it's a girl" or whatever and people would just simply tell any interested party.
The first millennial "thing" was to take to a relatively larger degree the previous practice of "wanting to be surprised" when the child is actually born. The reason why the technician asks is that there is a significant number of people who do not want to know until the child is actually born, not wanting to have the future gender intrude upon or influence their preparations.
Well, now it's gone in the other direction. People are openly doing either gender reveal memes or gender reveal posts, or going the even further whole hog and having gender reveal parties, in which they gather with wine and cake and invite all their friends and relatives, and then find a "creative" expressive "look at me" way to tell everyone the gender of their to-be-born child. Some people will hire a confetti cannon and shoot either pink or blue confetti. Some will burst a balloon revealing either a pink or blue balloon therein.
You get the drift. Silence everyone! Huge build up, drumroll, giant dramatic gesture, more wine and cake.
I'm personally torn on the practice. Part of me thinks of it is a narcissistic gesture by a generation that can't just go have a ham sandwich, it has to go somewhere where the menus are written creatively in chalk on black slates and have a farm-to-table braised pork reduction on artisanal baked rosemary and Himalayan rock salt foccacia.
But there's a part of me that kind of thinks that formally announcing, formally making a communal thing of preparing for a kid and/or making it an event kind of sweet.