France's pregnant first lady Carla Bruni-Sarkozy has sidestepped a question about the gender of her baby, saying she doesn't know whether she's expecting a boy or a girl.

Bruni-Sarkozy says the pregnancy was "unexpected".

Asked to confirm rumours it's a boy, she told Friday's Nice Matin daily, "I don't even know myself. There are things that are better kept secret".

The supermodel-turned-singer added she put plans to finish her third album on hold but she pledged the baby wouldn't derail her career.

Bruni-Sarkozy has a son from a previous relationship. Her husband, French President Nicolas Sarkozy, has three sons from two prior marriages.

The baby, which is due before presidential elections next year, is their first child together.