This.
I've read your update and you've hugged your daughter.
You said you want to gain control. The cat is out of the bag and so all you can do is deal with it now. That way you will gain control. I think someone earlier said just say Early days, don't want to discuss it atm. very firmly and move on.
You have a knotty ball of issues and can't fix them overnight but you can try unknotting them one by one.
Its clear that something happened at school. One minute you were friends with a group of mums - the next they all blanked you and you despise them. And you don't know why.
That really hurts, but I think you have to say to yourself, so what if they know? What are they going to do about it? The secret is out. Other than mention it. by tomorrow it will be really old news. If they are not that friendly anymore - they won't be that interested. Sad but true.
Unless you know someone who knows and will tell you, or ask one of them what happened, you won't find out. If it really bothers you, I don't think you have much to lose by asking. It might be something that can be fixed or you can cross it off your list of worries. If they are just mean girls and upset you, keep away from them and try not to think about them, it doesn't do you any good.
But bear in mind your daughter has to be in a class with these kids for the next 5 to 6 years and so it's better to be distant but civil. You don't need to be friends with them, but if your daughter can get along with them in school that is an advantage. But also helps her focus on other friends and activities outside of school.
I think if you know what your mother is like it was fairly obvious if she is a narc that she would behave this way and that this has upset you more than anything, but really if that is how she behaves and you know that in advance you need to distance yourself from her either physically or emotionally. You don't have to tell her much. Talk about the weather ( that's what I do with MIL, the weather, the latest News etc)
Finally. you need to sit down DH for a good chat on why he thought this was such a marvellous idea to tell everyone at just 5 weeks and why he didn't listen to you ( the actual pregnant person) when you said you didn't want to. And ask yourself if he often does this and perhaps think about what you want to do about that. It sounds like you don't have enough confidence in your own decisions and allow him to sway you, but he doesn't have to deal with the consequences in the same way that you do, so you have to listen more closely to your own inclinations and stand up for them.
I have noticed that some people have zero problem saying NO very very firmly and that this dissuades others from carrying on the argument. Maybe you need to practice this as there will be other issues coming up where you need to decide in advance what the best option is for YOU and then don't ask, tell. Advance planning is your friend. Decide how you want to spend your time in advance then people can't decide for you. Decide how you want your pregnancy to go in advance and so on. Obviously, if people are offering good advice (Doctors etc) then you need to listen, but if people are not listening to your opinion.. then you need to practice speaking up. That will make you feel more in control. Best of luck.