The reality TV star, 35, and her long-term partner 31-year-old Scott Disick are already parents to son Mason, 5, and 2-year-old daughter Penelope Scotland.
Kim’s big sister revealed her baby bump on Instagram, posting a picture of herself in a black bikini and jumping into a pool with friends.
READ: KHLOE KARDASHIAN IS FINDING KOURTNEY'S PREGNANCY 'HARD TO COPE WITH'
Reports suggest that, despite their happy news, things aren’t great between Kourtney and Scott due to his recent partying.
While the couple may have recently moved into a $14million mansion, it is thought that Kourtney has already kicked Scott out.
A source told In Touch magazine: “She’s made it clear to him that she’s sick of his partying. And unless he goes to rehab, she’s going to leave him.”
WATCH: KOURTNEY TELL SCOTT THAT SHE'S PREGNANT
READ: KIM KARDASHIAN ON ATTACHMENT PARENTING
These reports come after Scott was pictured having belated birthday celebrations, minus his pregnant girlfriend.
Speaking of Scott’s night out, a source told Radar Online: “He started smoking cigarettes and drinking beer. He seemed pretty wasted.”
Meanwhile, it was reported last week that Kourtney’s younger sister Khloe was finding her latest pregnancy hard to deal with. It is believed that, while Happy for Kourtney and Scott, Khloe can’t help but be reminded of her own fails at having a family after her marriage to Lamar Odom broke down.