Hello there! An author of omegaverse stories here! From what I have research and have written before, Omegaverse is inspired by the wolves, where there is the Alpha, the leader, beta, the followers and omega, the female in the group. But when it comes to Omegaverse in the fiction world omega can be potrayed as both male and female, also to Alpha and Betas. Hence, Omegas, when pregnant actually developes baby bumps because, pregnancy is still the same in the fiction world. My best guess to this manga is that, its the Mangaka's preference or style and I agree, this story does have a very amazing character developemantლ(´ڡ`ლ)
But this is from what I have researched and have used for my plotnof omegaverse stories, not 100% certain that this is the case.
Nice yaoi, character development, and art! Just confused though, when he’s pregnant why do I see no bump? Is that how it works in the omegaverse? No bump?