I wouldn't marry someone who'd announce it on Facebook. It'd be like if you leaned in for your first kiss, and they said, "Wait, let me Instagram this".
Lots of people we know do that / say that to people. A friend called me just last week telling me his wife was pregnant and to stay off of Facebook until they told everyone.
Most people comply - those that don't - get defriended.
What my SO and I did: Tell close friends and family by phone, then "announce" on FB so all the distant friends and family can learn about it.