"It must be a miserable existence."
^ This! ^
When I told my mother that I was pregnant with DS, she literally screamed at me. Read me the riot act, so to speak - I already had a child (DD, who was 7 at the time), how would DD cope with another child in the family, how unfair having another child was on DD, she (meaning my mother) would no longer be able to spoil DD in the way she always had done, everything DD had would have to be shared, she (meaning my mother) loathed my partner, and so on. My partner (who is now my ex) and I had known each other since we were 11 years old, and although he's not DD's biological father, he had - at that point - always been in her life (we were best friends at school, he supported me emotionally through my pregnancy with her and adored her from their first meeting when she was four days old... we started dating when she was a year old).
DS was very much planned and very much wanted, although to listen to my mother to this day, you'd think he was an "accidental pregnancy". I spent a lot of time veering hormonally between crying over my mother's seeming hatred of my unborn baby and being absolutely furious about it. It got worse when I miscarried his twin at 8 weeks, because of her vile behaviour (we knew I was pregnant from about 2 weeks and, stupid me thought that I could tell my own mother and be emotionally supported as, the previous year, I lost a - planned and wanted - pregnancy... in hindsight, though, we suspect she was quietly dancing a jig of glee at this loss). Ex-P was away at the time, it was Easter Weekend, I had been told I had to get complete bed rest by my midwife until I could get a scan arranged to see if it was a miscarriage or "a normal breakthrough bleed", and my mother announced that she was taking my daughter to her house for the duration... and left me completely alone for four days. She wouldn't even let me speak to my own daughter. I spent that time unable to get hold of Ex-P or any member of either of our families, terrified, and apart from our two cats, completely alone.
During the counselling I had after this experience, it was suggested to me that my mother reacted in such a negative, nasty way because she knew that she could control both DD and myself, if it was just the two of us. The moment I became pregnant by/had a child with my ex-partner, there was a loss of control. We would be "a proper family", which she wasn't the central focal point of (my DD has a medical diagnosis of NPD, and I suspect, if my mother were to submit herself for conversations with a trained professional, she would, too. She has to be the centre of attention at all times and woe betide the rest of us, her adoring minions - in her eyes we're all adoring, anyway... although it's just my father that actually is!). When I was 5 or 6 months pregnant with DS, she summoned (yes, you read that correctly) Ex-P to "a meeting" with her, where she attempted to lay down the law to him. And he (God bless him!) stood up to her and told her that she wasn't getting her own way over our family. As it turned out, he was actually completely useless when I was giving birth to DS and in the weeks immediately prior to/after (he actually moved back in with his parents so that he could be looked after properly... leaving me alone with a bump that still thought it contained twins, two cats and DD to take care of. But I managed, and my best friend stepped in and helped a lot, when I couldn't drive my DD to/from school, etc.), but I was not going to allow my mother that control which she'd actually had over us ever again.
She is miserable. Personality wise, I mean. She has no friends, her two sons won't have anything to do with her, she's not seen her eldest grandchild (DB2's son) since he was a toddler, she's never met her youngest grandchild (DB1's son), she'll never meet her first great-grandchild who is due in April (and probably not any that might follow), her only granddaughter (DD) holds her in contempt despite the pandering to/spoiling of, and my DS knows she doesn't love or even like him... and returns that. She has my father (whom she treats appallingly), she sees me very rarely even though I live five minutes away from the house I and my brothers grew up in, she has no hobby, no job... nothing. It has to be a miserable existence - but it's the one she built for herself.
OP, congratulations on your pregnancy. I hope your husband has your back in this, and that your MIL isn't anything like my mother towards you and yours. 