The 36-year-old actor and Kunis, 31, were hoping the 'Black Swan' actress would go into labour while he was on a break from filming 'Two and a Half Men'.
"They were hoping the baby would come this week because he's on hiatus. He (Kutcher) is a nervous wreck," a source said.
Ashton alluded to his pre-baby jitters on Twitter on Thursday, writing, "Nervous is excited's victim sister."
The couple, who got engaged earlier this year and started dating in 2012, are planning to get married after their baby's birth.