Gestation is the period of development during the carrying of an embryo or fetus inside viviparous animals.[1] It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time, for example in a multiple birth.
The time interval of a gestation is called the gestation period. In human obstetrics, gestational age refers to the fertilization age plus two weeks. This is approximately the duration since the woman's last menstrual period (LMP) began.