Saw it, found it interesting, thought I'd share.
https://www.instagram.com/reel/CuYa3LhAyNV/

Thanks for posting that. This is the evidence I have been looking for.

See this video: https://www.youtube.com/watch?v=hc3fS5aPxkA

The video eventually talks about "stealth" pregnancy. It says that what can happen is the baby ends up in the rib cage so a big belly never forms.

Take it with a grain of salt. If you google "stealth" pregnancy (or Wiki), they don't say anything about the baby being in the rib cage or anything like that. (I think part of it is they're trying to be PC. All the links I looked at talk on and on about how "some larger mothers" are more likely to have a stealth pregnancy... that and women who are in denial or have other psychiatric conditions! But, as we see in your video, relatively thin women can have this, too!) I do not know the sources for the video... they could be making it up.

I like the "rib cage" explanation and it seems like the only really good one --- either that or "Natural selection likes women with sexy round bellies, but some don't have the gene."

Next time they should do some kind of fancy MRI or whatever so we can see something like an x-ray video of where the baby is. That would either prove or disprove the rib thing. (I'll wait...)

My wife was afraid she wouldn't get a bump because she has a tilted uterus. Because it is leaning back it could cause most of the growth within the torso and not go out, just go up. It usually corrects itself after 1 pregnancy.