I'm no expert. We didn't have one of these parties. Never even heard of them till more recently but aren't they called "Gender reveal" parties or announcements?
DICTIONARY
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gen·der re·veal
noun
DICTIONARY
Search for a word
gen·der re·veal
noun
- a public announcement by expectant parents of the sex of their unborn child.
"they had their son play a special part in the gender reveal of their third child"