According to The Gorilla Foundation, as of 2014, Koko the gorilla has not yet had a baby, nor has she ever been pregnant. She is in her mid-30s, so she has a few more years of fertility ahead of her.
Koko has access to a male gorilla, Ndume, who is capable of producing offspring; however, she does not seem interested in mating. They do not live in a large social group like gorillas in the wild, and this is one possible inhibiting factor. Also, the two do not often have much privacy, and this appears to be important to some gorillas. Artificial insemination is not a viable option because it has not proven to be successful with gorillas in captivity.