I'm pretty sure the kind of people that do these parties are already going around telling their families and friends (and probably internet strangers) that they were having unprotected sex on the regular, no need to have a party to reveal what you've already told everyone
Sex party is a much better term. Baby’s don’t have a gender yet.
Preliminary gender assignment party.
Sex reveal party.
Sex party obviously has some differing connotations that are very innapropriate in the context of babies.
How, do you believe, babies are made in the first place?
Sex reveal party, revealing we had sex
I'm pretty sure the kind of people that do these parties are already going around telling their families and friends (and probably internet strangers) that they were having unprotected sex on the regular, no need to have a party to reveal what you've already told everyone
It's also great for advertisement.