The Kardashian-Jenner family stripped down for a photo shoot campaign promoting the Calvin Klein brand's popular underwear line.

>> Read more trending news

While Kourtney Kardashian, Kim Kardashian, Khloé Kardashian and Kendall Jenner bared their midriffs in the photoshoot, 20-year-old Kylie Jenner covered hers up with a red and white quilt. In other shots from the shoot, Kylie Jenner — well known for showing off her figure — kept her stomach hidden at all times.

Amid rampant speculation that she's expecting a daughter with her 25-year-old boyfriend, rapper Travis Scott, the young makeup mogul has made few public appearances and stayed off social media almost entirely. Some fans of the reality stars claim that Kylie Jenner has actually been the surrogate for Kim Kardashian West and Kanye West, who welcomed daughter Chicago West last week.

Related: Kim Kardashian, Kanye West welcome third child via surrogate

Khloé Kardashian, 33, confirmed her pregnancy with Tristan Thompson in December before going on a media tour, where she was unsuccessfully pressured to spill news about her younger sister's pregnancy.

Considering there’s no hint of a bump for Khloé Kardashian or Kylie Jenner in the underwear shoot, it’s possible the shoot was completed long before Khloé Kardashian’s bump reveal and Kylie Jenner is likely much farther along than her big sister, who confirmed that she’s six months along in early January.

Related: Khloe Kardashian confirms pregnancy: ‘My greatest dream realized’

While the older Kardashians are willing to chat up a storm about their own babies, it looks like the youngest of the group is going to maintain her radio silence.

"Kylie wants to disappear and be out of the spotlight and focus on her health and happiness," a source told People late last year. "Kylie isn't going to publicly address her pregnancy until she gives birth. She's not doing any public appearances and just wanted to take six months off."

What You Need To Know About Kim Kardashian