Well, if Christa decides she's not going without Omid, it would be killing all three of them (assuming she's pregnant) if you don't take him. Essentially you are deciding to leave her to the evil people and walkers...she would wind up having to leave him when he died anyway and would then be all alone with a screaming baby.....not good
You take them both, the lame guy and the pregnant chick. The group moves slower because of the infection, Omid probably turns and has to get killed anyway but maybe he gets a chance to infect another group member *shrugs*. Then Christa has to go into labor and make a lot of noise giving birth...resulting in a screaming baby that the group is saddled with that will alert walkers of your presence.
Shoot Omid, either let Christa come or let her be pissed off and go on her own. Repeat screaming baby/labor issues if she comes.
Gee none of it looks good does it?
I kinda like Christa but if she's pregnant, I say kill them both.