'KUWTK' First Look: Khloe Kardashian Endures Pregnancy Complications

Khloé Kardashian has gushed over her "easy" pregnancy thus far, but in a tense preview for Sunday's episode of Keeping Up With the Kardashians, the mom-to-be details a scary pregnancy complication.

In the promo, which can be seen here, Kardashin lies on a couch while sisters Kim and Kourtney Kardashian worriedly look on.

"Literally, I like can't walk," Kardashian tells her sister in pain.

"Can you text your doctor right now?" Kourtney asks as a worried Kim stares at Kardashian.

While the sneak peek didn't divulge any more information, all will be clear after Sunday's upcoming episode.

Kardashian, who is quickly approaching her due date, announced her pregnancy with NBA boyfriend Tristan Thompson in January after months of speculation. In an interview for Lorraine, she said she waited to make the announcement because "people just became so obsessed."

"Honestly, at first it's not safe to say anything and the doctor was like, 'I would just want to wait, for you.' So I was listening to doctor's orders," the KUWTK cast member said.

"And then people just become so obsessed," she added. "And I'm like, 'Trust me, you guys are all going to know eventually — I'm just waiting until it's the right time.'"

She admits, "But it feels good to announce and now be in tight clothes and feel like it doesn't matter anymore."

The complication featured on the KUWTK sneak peek could be Kardashian's first, as she said on Lorraine that she is "lucky" for having such an easy pregnancy thus far.

"I feel so lucky … I hear horror stories, and mine right now has been really easy," Kardashian explained.

"The very beginning is challenging because you feel so out of place … and I think you're the most sick and no one knows you're pregnant," she adds. "I'm not sure what the end is going to be like, but for right now, I'm doing pretty well."

The 33-year-old has stayed physically active throughout her pregnancy, despite her mom Kris Jenner's attempts to stuff her full of doughnuts.

"I give into cravings if I have them. Like if I want a doughnut, I'll have a doughnut. I'm not super crazy," she said. "My mom brought me like eight boxes of Krispy Kremes and got mad I didn't eat all of them. But I think that's crazy. But I definitely will eat sweets if I want and give into that but I really believe in working out and staying healthy. Every pound I put on I gotta take back off."

Despite her relatively easy pregnancy, Kardashian admitted that she once considered surrogacy after so many told her pregnancy wasn't in the cards for her.

"I mean, I thought about surrogacy at one point but then it just didn't cross my mind," the 33-year-old said. "And then when I got pregnant, I was just so surprised…When you hear all of these things about yourself, you just start believing them and I was just in shock I think as much as everybody else."

If Kardashian would have gone through with her initial plan to look into surrogacy, she wouldn't be the first of her sisters. Kim and Kanye West recently welcomed their daughter Chicago West with the help of a gestational carrier in January.

Kardashian won't even be the second sister to welcome a baby in 2018; sister Kylie Jenner and boyfriend Travis Scott announced the arrival of their daughter, Stormi Webster, earlier this month.

Soon it will be Kardashian's turn to become a mom — and she couldn't be more excited.

"I think it puts so many things into perspective and I mean, people say once you have a baby, your life just begins and you're going to realize everything you were doing is nonsense. But honestly, I'm so happy that this is happening in my life right now. They always say when you're ready you'll have a [baby], I feel so ready. What else can I even do? I'm ready. So, I feel like the timing really is perfect. I mean, it's just going to be so exciting everything that's about to happen," she said.

Keeping Up With the Kardashians airs on the E! network Sundays at 9 p.m. ET.