Gestation's the carrying of an embryo or fetus inside a female viviparous animal. Mammals duringpregnancy can have one or more gestations at the same time (multiple gestations). The time interval of a gestation plus 2 weeks's called gestation period, and the length of time plus 2 weeks that the offspring have spent developing in the uterus's called gestational age. (The extra 2 weeks's because gestational age's counted starting from the last menstrual period (LMP), rather than actual conception.… (More on Gestation)