MPreg, or male pregnancy, is an alternative trope often found in fanfiction and romance genres, and its role in plot development tends to revolve entirely around tension.
You can find it in certain omegaverse stories, though personally I gravitate toward those with a psychological focus. The central conflict rarely hinges on the physical improbability; the plot's engine is the relationship. In a fic like 'Tender Union,' the main character's pregnancy isn't simply a twist. It triggers existing political alliances to fracture, forces the protective alpha to question his own dominance, and pushes the usually reserved omega into a position of unexpected bargaining power. The external threats—family disapproval, societal scorn—are heightened because of that vulnerability.
It also demands a certain pacing. The narrative has to accelerate emotional intimacy. You can't have a glacial slow-burn when a biological clock is literally ticking. This can lead to forced proximity tropes and rapid declarations that would feel unearned in other settings. A reader looking for that accelerated, high-stakes relationship development often seeks it out for exactly this reason.
For me, the best executions treat it as a crucible for character, not a novelty. The plot bends around this central fact, testing loyalty, redefining strength, and ultimately deciding what kind of family the characters choose to build.