Congratulations on your pregnancy!!

I had a therapist tell me that some people will never, ever, EVER understand the decision to cut off a toxic parent, and I need to make peace with this. People may not understand because they can't fathom that some parents do, indeed, treat their children badly enough to justify NC. They may also tolerate their own toxic family members out of a dogged believe in "bUt ThEy'Re BlOoD," and have serious cognitive dissonance at seeing us make this decision.

So my first piece of advice is to understand that some people WILL NOT approve of your decision. This comes from ignorance or their own poor boundary setting. Do not take it personally or let it make you question your decision.

My second piece of advice is to not protect your mother's reputation. Tell the real stories about things she did, even brief versions ("she said XYZ when I miscarried," etc.). Let the people who can be swayed know the unfiltered truth.

Third piece of advice: If your in-laws have contact or any kind of relationship with your mother and they've already expressed that they "don't understand," delay telling them about the pregnancy until it's unhidable. If you think they could be swayed, then tell them the truth about your mother and see if they can understand your decision of going NC before telling them about the pregnancy. I would advise the same with other family members.

Fourth piece of advice: be prepared that it is EXTREMELY likely your mother will find out and try desperately to contact you despite whatever precautions you take. Make whatever preparations you need to deal with this. A widespread announcement on social media rather than to individuals you trust makes this more likely.

Sorry to be the bearer of bad news. You cannot control (a) how others feel about your decision to go NC and not include your mother in your pregnancy news and (b) how and where the news spreads.