All cetaceans are mammals; therefore, their calves grow within a placenta inside the mother’s body and are fed milk during the first months of life. The gestation period varies among species and may last from 11 to 12 months for mysticetes or 10 to 15 months for odontocetes.

Cetaceans are generally top-of-the-food-chain animals; thus, they have few natural predators. Therefore, the growth of whale populations in the oceans may be used as an indicator of the health of marine environments and availability of biodiversity for the future.

As with other mammals, the mother teaches their young how to survive, and this behavior is especially true in odontocetes. In most dolphins, an offspring stays with the mother for approximately two years. Orca calves stay with their mothers throughout their entire lives, with their mothers teaching them how to feed and communicate

It is rare for whales or dolphins to have twins. The offspring require a large amount of energy from their mothers, and females are generally incapable of feeding two or more offspring at the same time. In rare cases where twins are born, one usually does not survive, which is a reason why cetaceans deserve special care. Because females produce one offspring per pregnancy and require periods of between two and six years before their next pregnancy, cetacean populations do not grow quickly, and these animals are more vulnerable to environmental impacts.