A quotation from the source says..

According to the source, Kanye was overcome with emotion when Kim told him the good news.

“He’s like really on one right now and I don’t know if I should say this, but [Kanye] was crying when Kim told him she was knocked up,” the source reveals.

The source also adds, “I heard he got on his knees in front of Kim, she rubbed his head while he was crying and he was kissing her stomach. Guess he was overwhelmed at that point and couldn’t believe he’s about to be a father.”

Source:http://blog.zeeders.com/2013/01/01/kanye-west-cried-when-kim-kardashian-told-him-shes-pregnant/