Making his directing debut,writer/director Michael McCullers (who previously wrote the second and third "Austin Powers" movies) doesn’t help matters, shifting the tone of his screenplay between boorish bathroom humor, corny musical montages, and forced emotional confrontations without much concern for continuity.

Steve Martin is sublime as Kate's boss, Barry, purveyor of organic food and Zen koans. Even slyer is Weaver as the smooth-talking director of an exclusive surrogacy clinic who cheerfully explains that a surrogate is just a prenatal nanny. Funniest, though, is Romany Malco (Knocked Up) as Oscar the doorman, who becomes Angie's confidant.

Of course, Kate and Angie have the obligatory male romantic interests: Kate finds romance with Greg Kinnear's smart-alecky Rob, who runs a Super Fruity juice bar. Dax Shepard acquits himself with the usual dimpled charm as the bottom-feeding common-law husband. Fey and Poehler have considerable comic chemistry as the career woman and the surrogate mother, and Baby Mama keeps the laughs coming with bathroom humor, designer baby names, fertility-flaunting mamas and paternity tests - predictable odd-couple high jinks.

While there are some surprises, for the most part, the film is as predictable as that brief description makes it sound. It would have been great, however, for the film to be pushed into more challenging territory.