Gender announcements?

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Hey! We have great timing on when the gender ultrasound appointment is (near Christmas!!)

It's an easy opportunity to do a small, but cute, gender announcement.

BUT

How does that work? Do some companies "know the drill" when you send in the note from OB, or do you have to designate someone to know ahead of time so they can order what's needed?

Thank you! It's my first time doing one of these.