Ashlee Simpson has bought six pairs of size zero jeans to motivate her to lose weight.

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The singer – who is expecting her first child with husband Pete Wentz – is reportedly so worried about shifting her post-pregnancy pounds that she purchased the tiny trousers to help her stay focused.

A source told the National Enquirer magazine: “Ashlee broke down in tears at a doctor’s appointment in early August when she found out she’s gained more weight than is considered in the healthy range.

“She went straight to the Planet Blue shop in Los Angeles and bought six pairs of size zero jeans. She can’t wear them now, but she hopes it will give her the incentive to watch what she eats.”

Ashlee, 23, recently revealed she “can’t wait” for her baby to be born. She said: “We’re getting the nursery ready. I can’t wait to be a mom and he can’t wait to be a dad, so it’s fun.

“I have the greatest husband. He’s so awesome. It’s fun to have somebody that I love to do this with. The baby is my main focus right now. We’re both so excited. I mean, this is definitely the happiest moment in my life.”