French advertising agencies are seeking to exploit a wave of gossip about First Lady Carla Bruni's rumoured pregnancy, poking gentle fun at a story she has refused to confirm or deny.

The 43-year-old supermodel-turned-singer married President Nicolas Sarkozy in 2008 and has since given birth to an album of self-penned ballads but no new heir -- despite repeated rumours.

With Sarkozy languishing in the opinion polls and facing a tough battle for re-election next May, speculation is again rife that the Italian-born heiress may be carrying a pre-poll surprise.

Bruni herself did nothing to slow the rumour mill last week when she told an invited panel of readers of Le Parisien newspaper that her "lips are, in a sense, sealed" when asked about a pregnancy.

The French press is traditionally more respectful of the private life of public figures than its British or US counterparts, but that has not stopped advertisers from profiting from the buzz.

"So, Carla, do you feel like eating strawberries, or not?" asked a mother's wear firm in the pages of Liberation, referring to the popular theory that expectant mothers crave soft fruit.

Meanwhile, a car firm marketing a new minivan asked: "Dear Madame Bruni, would you perhaps be in the market for a family sized car?"

Sarkozy, 56, has three sons from previous marriages, and Bruni a 10-year-old son with the philosopher Raphael Enthoven.