The gossip site reports that Tristan was there as were her sisters Kourtney and Kim, mum Kris, and Khloe's best friend Malika. He and Kardashian dated in 2014 after she split from ex-husband Lamar Odom.
The baby girl was said to be due in late April.
Thompson's appearance comes after sources say he was cheating on Kardashian.
After two days of drama over the #Tristan Thompson cheating scandal, it looks like reports that Khloe was in labor were true. She begged to come back to L.A. and tried to find any way to make it work but her doctor wouldn't let her.
The website broke the story after obtaining a video that showed the National Basketball Association star kissing strip club worker Lani Blair.
Netanyahu concerned over Trump's plan to withdraw from Syria
A US withdrawal would create an Obama-style vacuum that would be filled by Iran, Hezbollah, Russia and the Assad regime. We've got more newsletters we think you'll find interesting.
Videos emerged on Tuesday, which apparently showed the sportsman being unfaithful as recently as last weekend.
Khloe and Tristan have been dating for well over a year, but their current relationship status is questionable as she and the Kardashian clan determine if Tristan really cheated or if he was "set up".
Kardashian, 33, did not publicly confirm she was expecting until she was nearly six months pregnant. Plus it'll be literally so adorbs to see Khloe's daughter playing with Stormi Jenner, Chicago, Saint and North West plus Mason, Penelope and Reign Disick.
A source close to family did reveal that Khloe was devastated and her whole "entire world has been turned upside down". Allegedly, he spent time with her at a club that evening and didn't want the night to end. Well, this is a time to be happy, as Khloe has just become a mommy! "I had been waiting and wondering but God had a plan all along".
"He knew what He was doing", she wrote. "She never had any reason to not trust him". "I like people's opinions in this aspect because someone might have something that I love.I have no rules or restrictions yet on names".