I was pregnant in 2010 and 2013. Looking at google trends, these were BARELY a blip during my first pregnancy so I didn't give it any kind of thought. Nobody did this. Sometimes if you were nuts you'd wrap a photo frame for your parents with an "it's a girl!" message or something because grandparents like surprises. But nobody had parties or had an ultrasound tech put a secret message in an envelope for a bakery's eyes only.
In 2013, I remember these becoming an idea that was discussed in pregnancy forums, but I immediately knew it was not my thing. First, you're not revealing gender since that's a construct, you're revealing anatomy. So my sister and I joked that instead of pink or blue, the theme of the party should be inspired by genitalia shapes, right?
But now they seem to be a required THING during every pregnancy, and the sex of a fetus is determined like the day after a woman passes a pregnancy test through some blood chromosome workup or something, instant! Then you have months to plan the party!
Compare that to past generations... I know a woman who had twin boys in 1978. Not only did she not know she was having boys, she didn't know she was having twins.
So that's why I'm here to say that the world has changed and BACK IN MY DAY I had to wait until the terrifying 18-week anatomy scan before I figured out what sex my babies would be. In both cases, my mother's intuition told me I would have boys. In both cases, I was wrong.
Here are the links back in time to those entries. One post about my thoughts before the scan, and then a "big reveal" where I just wrote in my livejournal what I was having and then everybody moved on with their lives.