Singer Gwen Stefani has revealed that she is obsessed with her weight, saying she went to extraordinary lengths to lose the weight she gained during her pregnancy.

Speaking to Elle magazine, the singer said: "I worked out with my trainer throughout the whole pregnancy until about two weeks before."

"I cried during my last session. I was like, 'I can't breathe, I can't do this any more. What am I doing?' It was crazy."

"All of my life I've had to work hard to stay in shape. I've always struggled with it. I was a little chubby when I was younger and I didn't want to be that person forever."

"There aren't any tricks, it's simple maths - you put this much food in, you burn that much working out," she said.

Stefani and husband Gavin Rossdale welcomed their baby son Kingston eight months ago.