Directing and script make 'Baby Mama' a difficult delivery

The biological alarm isn't just ticking in "Baby Mama," it's ringing so loud that single career woman Kate (Tina Fey) will do anything for a bundle of joy. With adoption out of reach and her own reproductive chances "one in a million," that means a surrogate mother for her otherwise fertile eggs. Or, in the words of the surrogate pregnancy entrepreneur (Sigourney Weaver): outsourcing.

Enter Angie (Amy Poehler), a South Philly high school dropout with a low-watt loser of a common-law husband (Dax Shepard) and a junk-food diet. The trajectory isn't all that hard to predict: Angie leaves her white-trash hubby and moves in with Kate, where odd-couple collisions and decidedly unusual pregnancy complications ensue.

The friends and former "Saturday Night Live" collaborators make a good odd-couple buddy comedy team. Fey underplays the uptight corporate professional with a frozen half-smile whenever she slides out of her narrow comfort zone and Poehler exuberantly overcompensates as the trashy woman-child who still acts as if she's a sassy high school girl and is stymied by a child-proofed apartment.

It's just that broad comedy isn't always suited for their brand of improvisational give-and-take. Writer/director Michael McCullers sprinkles the film with sight gags and comic characters (the lisping birth coach becomes funny out of sheer doggedness), but his pacing is poor and doesn't know how to showcase the small-screen chemistry of Fey and Poehler on the big screen. The plodding script and the plot twists tossed in at predictable intervals don't help them much.

The supporting cast helps distract from the inevitability, from a chirpy Weaver to Romany Malco's incredulous doorman, to Steve Martin as a shamelessly name-dropping corporate guru with a silver ponytail. That's a lot of midwives for such a conventional delivery.