Also, because roman is dead, it means that the story takes place at day 259 at the very earliest. (Assuming roman left the pitstop right after shel left or killed Stephanie, and immediately got himself killed.)
That's 8 2/3 months into the apocalypse.
Christa's unborn baby was probably conceived around day 0 (its unlikely Christa and Omid would have taken any risks with the apocalypse going on). Any more into the apocalypse wouldn't make sense, any less, and it would have been obvious just by looking at her.
What I'm saying is that there is a very good possibility that Christa is about to or recently did give birth to her baby. You notice how Telltale only showed a close up of her face? If they had the whole picture, she probably wouldn't be pregnant any more.