Jenner had one hand placed on her hip, lifting her top to reveal just a hint of her stomach.
The makeup mogul posted another photo with several girlfriends on Sunday posing in bath robes.
"Mornings," she captioned the mirror selfie. Any signs of a bump were carefully obscured by the mirror frame, reports news.com.au.
Fans have demanded Jenner put them out of their misery with an official announcement.=
Walking around the city with friends on the weekend, Jenner ditched her usual skin-tight outfits and crop tops and opted for a loose-fitting dark grey T-shirt and brown jogging bottoms, finishing the casual look with white trainers, according to The Sun.
She was spotted with a group of friends backstage at iHeart Radio Festival where her boyfriend was performing, linking on to her pal's arm as they walked through the area.
Kylie and Travis have been dating since April and their romance was officially confirmed at the Met Gala on May 1.
Speaking of her pregnancy, a source reportedly told The Sun: "They started telling friends a few weeks ago. The family has known for quite some time. She is really excited and so is Travis!"
Another insider added: "It is an unexpected but completely amazing turn of events that she could not be more excited or thrilled about.
"Everyone is overjoyed for her. This is the happiest she's ever been."
Sources claim the baby is due in February.
Shortly before the news broke, Kylie revealed she keeps a list of names for her "future kids" on her phone.
Writing on her website thekyliejenner.com, she shared: "I keep a list in my phone of names I like for my future kids. But they're my secrets for now!"
The star who appears to live much of her life on social media also once pledged to delete her apps, ditching her 97 million followers once she had a child.
She shared: "Once I have a kid, I'm not going to be on Instagram. I'll probably delete my Instagram and just ... I don't know, live life.
"I would love to have a family and build a home with a farm in Malibu Canyon and just have my kids and throw away my phone, and just really, like, live my life and not do this anymore."
