When Tina Fey discovers her inside ladyparts are broken, she recruits Amy Poehler to house her fetus, which, for some reason, also means they have to live together. Something like Dupree (of You, Me & fame), Poehler proves herself a crass, slow-witted, disgusting houseguest, and ends up teaching Fey an important lesson in childrearing (that caring for a child is much like having a white trash boarder) and friendship (I guess).
It it feels like you're saying "man, another pregnancy comedy?" as much as "man, another pregnancy?", I know exactly where you're coming from. But like Knocked Up and Juno before it, Baby Mama might have the talent to make it worthwhile, with the former Weekend Update anchors in lead roles. Plus, they've given it a new spin, where instead of treating the child as an unwanted mistake, they take the farcical path of pretending pregnancy could be not just allowed, but desired--sort of a prenatal Bizarro World for the child-fearing.*
*Apologies to happy parents and those who don't consider impregnating someone a top-five fear.