Her rapper boyfriend Kanye West first revealed the news during a concert in Atlantic city, New Jersey, when he said: "Stop the music and make noise for my baby mama." He was referring to Kim, who was in the crowd.
Later Kardashian, 32, posted the revelation in her blog, titled "New Year, New Beginnings", reports aceshowbiz.com.
"It's true! Kanye and I are expecting a baby. We feel so blessed and lucky and wish that in addition to both of our families, his mom and my dad could be here to celebrate this special time with us. Looking forward to great new beginnings in 2013 and to starting a family. Happy New Year," Kardashian posted.
Her pregnancy was suspected early December 2012 when West was seen accompanying Kardashian to an obstetrics and gynaecology clinic.