Credit: Ray Tamarra/Getty

With the Kardashians, it's not always easy separating fact from reality show fiction.

One thing that's absolutely bonafide? Khloe Kardashian's fertility problems. "Khloe is having major problems getting pregnant," a pal tells the new Us Weekly. Her struggle to conceive with hubby Lamar Odom is "very, very real," the friend adds. "It's not contrived for their reality show."

And now that big sister Kim is married to Kris Humphries -- with a baby atop their priority list -- Khloe, 27, feels the pressure even more acutely.

"If Kim were to get pregnant first, that would cause tension, because it would highlight Khloe's struggle," a show insider explains.

Indeed, although Khloe has said "I'm a big believer in God's plan," another pal says she may just be putting on a brave face.

"There is some friction now because Khloe knows [Kim's pregnancy] is the next step and she feels terrible she can't get pregnant herself."

(Eldest sister Kourtney, 32, who has son Mason, 21 months, is also eager to get pregnant again with beau Scott Disick.)

"The competition has really got her depressed," the insider says.

For more on Khloe's baby pressure, pick up the new Us Weekly -- feature 50-plus bonus pages of fall fashion -- on stands Friday.