THE early scenes in Juno have the trademarks of those calculatedly quirky indie productions that are magnets for North American film festivals, emerging out of nowhere for their moment at Sundance, only to disappear just as quickly.

Juno opens on a brightly coloured credit sequence over the first of many catchy tunes from Kimya Dawson, and all the characters speak in hipster one- liners that are funny but feel contrived. Sixteen-year-old Juno McGuff has a hamburger-shaped phone and says that her father named her after the Roman goddess who was "really beautiful and really mean, like Diana Ross".

But then we get to know Juno (played by the vibrant, irresistibly appealing Ellen Page) and the characters surrounding her. And as we begin to care about them all, first impressions are rendered misleading.

The fourth recent movie to take an unplanned pregnancy as its turning point, it introduces Juno as a bright, confident and disarmingly frank pupil at Dancing Elk High in Minnesota. Driven primarily by curiosity, she and her fellow student, a track athlete, endearingly played by Michael Cera, engage in sexual experimentation after school.

When Juno discovers she's pregnant, she impulsively sets out "to procure a hasty abortion", but changes her mind. Believing she is too young for motherhood, she decides to find adoptive parents for her unborn baby.

Juno's quest leads her to a childless couple, Mark and Vanessa Loring (Jason Bateman and Jennifer Garner), who live in comfortable suburbia, but the movie would be far less interesting if everything was so easily resolved.

Given that this coming-of-age story draws its teen characters so sympathetically, one suspects that the Lorings are being set up as the butt of the humour as soon as we see that they live in one of a row of identical houses in Glacial Valley Estates.

First-time screenwriter Diablo Cody surprises again when she digs beneath the surface of the Lorings and engages with them. She extends the same affection to Juno's father (JK Simmons) and stepmother (a radiant Allison Janney), who, after their initial alarm at Juno's news, prove solidly supportive. Still, there is nothing idealised about this movie as it follows Juno over nine eventful months and turns more serious as the birth of her baby looms.

Following his assured feature debut with Thank You for Smoking, director Jason Reitman nimbly steers the characters through the many complications in Cody's fresh, imaginative screenplay for a seductive movie that sparkles with wit and warmth.