Baby Mama is a bundle of laughs, just don't expect anything too deep.

Given the plot of a 30-something, single career-woman desperate to have a baby but who discovers she's infertile and looks to surrogacy as the answer, there was so much more depth that could have been generated through the exploration of infertility and its emotional ramifications.

Instead the movie skims along the surface, relying on humour to sell the story, which it does fairly successfully.

Mean Girls maths teacher and screenplay writer Tina Fey is great as Kate Holbrook, the anal-retentive, health conscious vice-president of an organic food company, who has been given the task of setting up a new store, ``her baby'' as the funny, hippie boss Barry (Steve Martin) explains.

Little does he realise that Kate's obsessed with bearing her own child. She's attempted IVF and is devastated when a nerdy doctor says her T-shaped uterus means she has a one in a million chance of falling pregnant.

She consults Chaffee Bicknell (Sigourney Weaver) who runs a surrogacy service for a fee of $100,000 and is assigned ``white trash'' baby carrier Angie (Amy Poehler). The party-girl is married to ignorant Carl (Dax Shepard) who provides a much stronger performance than his earlier effort in the pathetic Smother.

When Angie and Carl break up, she moves in with Kate and the sparks fly.

There's a chemistry between the actors that ensures their scenes are dynamic, and are complemented by an upbeat soundtrack.

Angie is the total opposite of Kate - she loves junk food, alcohol and karaoke, and has some unusual habits like wearing her name on her belt and farting in purses.

Naturally there are plenty of arguments as the two adjust to living together, but gradually they become friends.

Meanwhile, Kate develops a relationship with charming lawyer turned juice-maker Rob (Greg Kinnear) and Angie's not being quite as truthful with her new friend as she should.

Baby Mama is entertaining and fun, but it lacks depth and the ending is too contrived. Director Michael McCullers could have done so much more with the script.