Why certain people get baby bumps? Did we ever find out?

Ik im going to get a lot of backlash for this but

I’m rewatching for like the 100th time because I NEVER finished the show. I kept restarting for different people and ended up getting trapped with other shows. Long story short, why the heck does everyone get a baby bump but Maggie and Nabila? Even Michonne got one (Rosita ain’t included … I ain’t that far and don’t know if she had one). I’m in Season 9