The baby will join big siblings North, 5½, Saint, 3, and Chicago, 1 this month.
The impending arrival is said to be "heavily influencing" her sisters' pregnancy plans.
"Kim having another baby this year is heavily influencing her other sisters and their baby plans," a source told E! News.
"They all loved being pregnant at the same time and everyone wants all of the kids to be close in age. Everyone jokes about having another round of 'triplets' all the time."
Last month Kim told E! News, "I definitely feel like we are more connected now, especially that Khloe's back and we're hanging out with all the babies.
"All the kids want to hang out. It's just a whole different experience now. It's so much fun."
Kylie also opened up about her desire to expand her family.
"Am I going to have another baby? I want another baby but, 'When?' is the question and I'm definitely not ready right this second," the 21-year-old told social media followers. "And I don't know when I will be, but when I do, I would love to share more of that with you guys."
The same is true for Khloe who is believed to want a sibling for True.
An insider told PEOPLE, "Things are up and down with Tristan, but she would like more kids with him. That's what she feels will make the most sense for True and their little family."