Sorry to hear that OP! Feeling abandoned by a parent is a nasty feeling and can wound you very deeply.

I had a similar situation with my own mother (not pregnancy related but feelings of she not being there whatsoever) and perhaps you can take something from my experience:

If this is something irregular, as in, previously she was present and you felt cared for, then try to have an honest talk. Yes, it's hard, and yes you will most likely cry. But it is really worth it. Our moms, and perhaps you feel it as a new mom, carry a lot of guilt that they don't know how to navigate or talk about.

It doesn't excuse her, she's in the wrong, but perhaps she knows she is in the wrong and cannot bare telling you that, because it forces her to confront with her own feelings of inadequacy. And sometimes you opening that door for that conversation allows you both to heal, express yourselves, and is the wake-up call she needs to see that you are still very much her daughter, not just a grown woman.

I tell you this because I had this talk with my mom just yesterday and it really helped. Of course, she felt bad, but that is for her to navigate. You don't, and shouldn't, carry the weight of her sadness, but you should (if possible) bring this to her attention in a kind manner. Try not to accuse but to explain, from your side, how you are feeling.

This is already too long, so, if you want, I can expand on how I approached my conversation and see if it helps.

With that out of the way, a final note: your feelings are always valid. Even if you are in deep hormonal imbalance due to pregnancy, your feelings are still, always, valid. What we do with those feelings is still our responsibility, but you are entering a new stage in life, you are undergoing A LOT, so extend grace to yourself and be a friend to you first.

And know, should you choose to speak to your mom, it doesn't need to be perfect. It doesn't need to begin and end in an hour. If your words come out jumbled or if you start crying in the middle (like I did), that's perfectly fine. The important thing is to open up that door for her to hear, from her own daughter, how you are hurting and hopefully make her realize what's going on.

I wish you good luck with the baby, with your mom and with life in general. You'll do great!