Viviparous animals are those that give birth to live young. In viviparous animals, both fertilization and the development of the embryo take place inside the female reproductive system. Once the fetus development is complete, the mother delivers the baby. This condition is referred to as matrotrophy where the embryo obtains the nutrients directly from the mother and not the yolk. Examples of viviparous animals include humans, dogs, cats, elephants, and most mammals.

There are two other methods of reproduction commonly used by animals, birds, and insects. These are oviparity and ovoviviparity. In oviparous animals, females lay eggs containing the embryos and placenta of their young. These eggs develop almost entirely outside the female’s body. Ovoviviparous animals also have eggs, but the eggs develop inside the female’s body and even hatch internally.