The period a mammal is pregnant is called the ______ period.

The term used to describe the period during which a mammal is pregnant is "gestation." This term specifically refers to the duration that an embryo or fetus develops inside the uterus of the mother, leading up to birth. The gestation period can vary significantly between different species of mammals.

In this context, "gestational" is closely related to gestation but refers more broadly to anything pertaining to gestation rather than the period itself. "Breeding" generally refers to the mating process rather than the pregnancy period. "Incubation," while familiar in the context of bird eggs, specifically describes the period in which eggs are kept warm until they hatch and does not apply to mammals. Therefore, "gestation" is the precise term that aligns with the context of pregnancy in mammals.