The 30-year-old clothing store owner, who is expecting a son in December, was nearly 300 miles away from her Calabasas home when thieves broke in and stole $80,000 worth of jewellery.
Kourtney was recovering from celebrating her sister Kim's 29th birthday on Friday night when the unknown assailants entered her home on Saturday morning.
Shock: Heavily pregnant Kourtney Kardashian was partying in Las Vegas on Friday night when her house was burgled
Los Angeles County Sheriff Sgt. Kristy Criner confirmed to People magazine: 'That's what was discovered missing in the initial investigation.
'Sheriff's investigators and our crime lab are responding on the scene.'
News of the break-in ended an exciting weekend for the blooming reality star, who joined Kim, R&B singer Ciara and their brother Robert Kardashian for the festivities.
Kim hosted a party at the Tao nightclub at the Venetian Hotel & Casino, where she was staying in a luxury suite.
Fashionable siblings: Kourtney flew to Vegas to mark her sister Kim's 29th birthday
Notably absent was Kourtney's boyfriend Scott Disick or their newlywed sister Khloe, who only got to Vegas on Saturday.
Khloe hit the headlines three weeks ago when she wed Los Angeles Lakers basketball player Lamar Odom after just a month of dating.
Despite being her final trimester, Kourtney has refused to swap her high fashion wardrobe for expanding maternity cothes.
She said: 'It's hard to get dressed when you're seven months pregnant almost. It's challenging but I still try to be fashionable.'
Just like her sister Kim, Kourtney opted for a figure-hugging cream jersey dress and black heels on Friday.
Birthday girl Kim, who recently reconciled with her American football player Reggie Bush after a brief split, showed off her famous curves in a sparkly dress and shoe boots.
Since announcing her baby news in August, Kourtney has been filling the US gossip magazines with every little detail of her pregnancy.
Kourtney split up with Scott, 26, earlier this year but they reconciled after finding out she was pregnant.
Birthday meal: Kim and Kourtney dined with (L-R) their brother Rob, Lala Vasquez, Ciara, Brittny Gastineau and Jonathan Cheban
Kourtney, whose rocky relationship with Scott featured on Keeping Up With The Kardashians, admitted the pregnancy was unplanned, but the couple were excited about becoming parents.
She said: 'This probably sounds so dumb, but there's so many times I'll forget to take my pill and I don't think it's that big of a deal. It's just so stupid.'
Kourtney said her famous family were thrilled when she told them she was expecting, but said her stepfather, former Olympian Bruce Jenner gave her a reality check.
She told Us magazine: 'He said, "You guys are acting like you're getting a little puppy dog! You need to take this seriously." He freaks me out the most.'
