The 37-year-old reality star and 40-year-old rapper expressed their gratitude in a post on Kardashian's website Tuesday after their surrogate gave birth to a baby girl.
"Kanye and I are happy to announce the arrival of our healthy, beautiful baby girl," Kardashian, who already shares 4-year-old daughter North and 2-year-old son Saint with West, wrote.
"We are incredibly grateful to our surrogate who made our dreams come true with the greatest gift one could give and to our wonderful doctors and nurses for their special care," she added. "North and Saint are especially thrilled to welcome their baby sister."
Kardashian and West's daughter was born Monday, Jan. 15, at 12:47 a.m. PT, although the couple have yet to announce the baby girl's name. Kardashian also shared news of her daughter's birth on Twitter.
"She's here," she wrote alongside a link to her blog post.
Kardashian and West confirmed in September that they were expecting their third child. Sources told Entertainment Tonight last week the couple are "fully prepared and can't wait to bring their baby home."