Answer:
Viviparous
Explanation:
I think that's the word you are looking for
Viviparous animals give birth to live offspring after they have developed in the parent's body
The opposite of this would be Oviparous, meaning an animal that lays eggs.(birds, etc)
Fun fact:
the echidna (also known as a spiny anteater) and the duck-billed platypus are the only mammals known to lay eggs!
