The newest edition to the recent slew of pregnancy comedies, “Baby Mama” stars Tina Fey as Kate Holbrook, a career woman who (much like real life) occupies a position of power in a business run mainly by men. Trim, snappy and bespectacled, Kate is a neurotically organized, wealthy single gal until the day she begins to see babies gurgling at every turn. Kate is suddenly envious of her sister (Maura Tierney), who has a horde of filthy lil’ cuties. Kate is, of course, overwhelmed at age 37 with baby fever, but cannot reproduce due to her unfortunately T-shaped uterus. What to do?

Enter Angie Ostrowisiki (Amy Poehler), a stereotypical blond white-trash answer to Kate’s prayers. Angie wears skintight pants, guzzles king-sized sodas, and is extremely fertile. But Angie comes with baggage: the abominable Carl (Dax Shepard), who so embodies the stereotype of white trash, he actually calls in to radio show money giveaways to earn a living. Angie needs to get rid of him, and Kate needs a baby. Opposites attract, so the saying goes, and this film is no exception; at its heart, “Baby Mama” is an old-fashioned buddy movie about friends who need each other to fulfill their unsatisfying lives. It’s nothing revolutionary, but were it not for the two female stars’ formidable comedy pedigrees, this film would most likely not exist.

Arguably two of the funniest women on the planet, Fey and Poehler have perfect comedic chemistry, perfected during their residence on “Saturday Night Live’s” Weekend Update. Fey is also a viciously funny screenwriter, penning “30 Rock” and “Mean Girls,” and as a result, one walks into “Baby Mama” with fairly high expectations. At first, the film seems like a disappointment. The pacing and the tone is unsettling; the film hovers between slapstick and caustic without ever hitting the right notes. But by the end, the film settles into its cheerful yet predictable storyline, and the stars rise above it.

Fey did not write the script, and her humor is rather underutilized, coming off as a bit stiff and wooden. The film also makes little use of the wonderful Greg Kinnear, who plays the type of useless hunk-in-waiting usually reserved for Patrick Dempsey. Steve Martin also appears as Kate’s ponytailed egomaniac boss, who orders her to build a supermarket inspired by a shell he found in an airport. But Amy Poehler really shines, softening her character’s rough edges with goofy flashes of brilliance. Whether she’s peeing in Kate’s bathroom sink or singing karaoke at full blast, Poehler’s Angie is wacky, childlike and compulsively watchable, both borrowing from and transcending her SNL sketch background and becoming a full-fledged star.

Writer and first-time director Michael McCullers does just fine handling this unapologetically mainstream comedy. However, one cannot help but wonder if the movie would have been sharper and funnier if Fey had written it herself. If penned by Fey, we might have had a delectable send-up of maternity comedies and the upper-class women who pay thousands of dollars for fertility treatments. Instead we get a feel-good narrative that preaches acceptance across class barriers.