Kim Kardashian West is ''on a mission'' to get pregnant.

The 34-year-old beauty - who has 20-month-old daughter North with husband Kanye West - is determined to have another baby so has been consulting with a fertility doctor to boost her chances of conceiving.

She said: ''I am so on a mission to get pregnant. I remember growing up being so close with my sisters, so I want siblings for North. Because it's been so tough I'm seeing a fertility doctor to see, like, exactly when I'm ovulating and really increase my odds of getting pregnant naturally.''

In order to boost her chances of getting pregnant, she and the 37-year-old rapper have been having sex as much as possible.

Speaking to her sister Khloe Kardashian on the premiere of the new series of 'Keeping Up with the Kardashians', she said: ''I've been having sex 500 times a day.''

Elsewhere in the episode, Kim - who had sex with Kanye in a bathroom before a photo shoot - also said: ''I was like, I'm ovulating today! So I made him come to my photo shoot.

''There's only a 20 percent chance of getting pregnant every month, I know that I'm ovulating right now, so you gotta get it in when you can get it in!''

And the blonde star also refused to move for some time after making love with her husband in a further bid to boost her chances of conception.

Asked by half-sister Kendall Jenner why she was lying in bed instead of sitting with her family, she admitted: ''The doctor said when I have sex I have to lay down for, like, 10 to 20 minutes, so, I just had sex before you guys got here. He said it takes 10 minutes for a sperm to swim up there. I'm going to wait like 5 more minutes just for this to marinate inside of me.''

Kim was seen feeling ''frustrated'' at how difficult she is finding getting pregnant again but later in the episode admitted she worried she was trying too hard.

She said: ''It's, like, so frustrating. I'm exhausted and I think I'm just making this all about the wrong things. Like, I'm forcing it, so we just need relax. We just need to not stress it, not plan so much, and just go with the flow.''