The rapper shared the news with hundreds of concertgoers during a show in Atlantic City, US last night.
He revealed Kardashian is about 12 weeks pregnant.
He told the audience to "stop the music and make noise for my baby mama" in reference to his girlfriend, who was in the crowd.
Kardashian's family took to Twitter to share their excitement.
Sister Khloe Tweeted: "KIMYE!!!!! Keeping secrets is hard with so many family members! Especially when you are so freaking excited!!!!! LOVE is everything!!!!"
Kourtney added: "Been wanting to shout from the rooftops with joy and now I can! Another angel to welcome to our family. Overwhelmed with excitement!"
Sister Khloe Tweeted: "KIMYE!!!!! Keeping secrets is hard with so many family members! Especially when you are so freaking excited!!!!! LOVE is everything!!!!"
Kourtney added: "Been wanting to shout from the rooftops with joy and now I can! Another angel to welcome to our family. Overwhelmed with excitement!"
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