you are well passed the point of announcing
There isn’t a unified “point of announcing”. No law, no social convention – some do it very early for support in case of miscarriage, some after the 12-week scan, some the 20-week scan. Some, like me and OP, and lots of people I know, not til there’s a baby.
And I’m not at all sure where pp are getting the idea that OP wants to be all stagey and SURPRISE about her baby and is pissed off that MIL has ruined that. It’s perfectly clear to me that being private around her pregnancy is borne out of anxiety and fear, but well done to all the shitbags on this thread for being dicks about it.
Given people can have friends worldwide it’s not totally wild to keep a pregnancy from your friends, intentionally or not – people who see you in person know, people who don’t, don’t. And not everyone wants to do a social media “reveal”. I use social media for idle chit chat and work and hobbies (eg “here’s my garden”), not personal life stuff.
FWIW, OP, when I announced my daughter’s birth not a single friend gave a hoot that they hadn’t known of the pregnancy. She and I were showered with love, joy, food and understanding. It’s a lovely memory.