The 'Keeping Up with the Kardashians' star, who has 18-month-old daughter North with rapper husband Kanye West, is desperate to have another baby, but says "it's been more challenging" than she thought it would be.
The brunette beauty said: "It's been more challenging to get pregnant the second time around."
Kim's battle to conceive will be documented on the upcoming series of her family's reality TV show.
She also told MailOnline at the E! International Press Junket in Los Angeles on Friday (09.01.15): "When you're not planning it, it happens. It's just how God works. And when you want it so bad, it's not happening..."
The star previously called North her "miracle baby" as doctors once told her she might never be able to get pregnant.
She told the January issue of Elle magazine: "A few years ago I was told I could never get pregnant. Three different doctors told me the same thing, which is why I wanted to have my eggs frozen. I was just about to do that when I found out I was pregnant with North."
The 34-year-old star was forced to deny rumours she was pregnant again last month, shortly after her older sister Kourtney Kardashian gave birth to her third child, Reign, with boyfriend Scott Disick.
The couple also have daughter Penelope, two, and son Mason, five.