BABY MAMA — *** — Tina Fey, Amy Poehler, Greg Kinnear; rated PG-13 (vulgarity, drugs, profanity, violence)

"Baby Mama" employs a number of former and current cast members from the long-running sketch comedy program "Saturday Night Live."

That may explain why at times this inconsistent but mostly likable comedy feels like an overlong skit from that show. In fact, the only reason it works as well as it does — or that it even works at all — is because of its star, former "SNL" head writer Tina Fey, who's really turning into an endearing comic performer.

She's also getting more confident in her acting abilities, as evidenced by some dramatic moments in TV's "30 Rock" as well as this vanity vehicle.

Fey stars as Kate Holbrook, a 30-something corporate vice president who desperately wants a child. Unfortunately, she's discovered that she is infertile.

But rather than wait to adopt, which could take years, she opts for a pricey surrogacy program. She thinks she's found the perfect "gestation assistant" in Angie Ostrowiski (Amy Poehler), who's more than willing to carry a child for Kate — as long as she gets paid, of course.

That partnership becomes uncomfortably close when poor white-trash Angie leaves her common-law husband, Carl (Dax Shepard), and suddenly shows up on Kate's doorstep.

This goofy "Odd Couple" character relationship is the movie's main focus, though there's also an appealing subplot about Kate's romance with a small-business man played by Greg Kinnear.

Screenwriter-turned-filmmaker Michael McCullers' directorial debut ends sort of messily and is pretty overstuffed — neither Holland Taylor nor Maura Tierney, who play Kate's mother and sister, respectively, get much to do.

But Steve Martin has fun as Kate's pony-tailed, new age-y boss; Romany Malco steals scenes as a sharp-tongued doorman, and Sigourney Weaver is amusing as the surrogacy program director.

"Baby Mama" is rated PG-13 for crude humor involving pregnancy and bodily functions, some of them sexual in nature (sight gags and references), drug content and references (intravenous painkillers, as well vitamins and nutritional supplements), scattered profanity, and some comic violence (including some slapstick and car vandalism). Running time: 99 minutes.

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