The 'Autobiography' singer - who recently announced her engagement to Fall Out Boy rocker Pete Wentz - is said to be expecting her first child in October.
A source close to the couple told America's OK! magazine: "Ashlee and Pete are as perfect for each other as any two people could be.
They don't spend a minute apart if they can possibly avoid it and are over the moon about the baby." Ashlee is believed to have been struck down with a nasty bout of morning sickness when she went to Malibu's Chart House restaurant to celebrate Pete's assistant's college graduation.
The source added: "Pete was clearly worried about Ashlee, and was holding her hand the whole time." Ashlee, 23, and 28-year-old Pete are hoping to tie the knot before Ashlee's baby bump becomes too obvious. A friend of the pair said: "They're planning on something in the Santa Barbara area probably by the end of May.
Ashlee would like to walk down the aisle before she's showing. She's very cute the way she's always checking out her belly now and asking everyone, 'Am I showing yet?'"
However, Pete has already denied the pregnancy rumours, telling MTV News: "There is a witch hunt for people to be pregnant whenever they get engaged in Hollywood. This is all news to me.
"I can't wait for the story about how I'm really in a gay relationship and this is all just a cover. This is crazy - I mean we're engaged, that's true, and we're happy about it."
Ashlee further fuelled pregnancy rumours yesterday (14.04.08) when she appeared to be hiding her stomach with her bag as she walked through Los Angeles' LAX airport.

Ashlee Simpson is reportedly pregnant.