Embryonic diapause is a phenomenon characterized by the temporary suspension of embryo development and delayed implantation in the uterus. It is an interesting reproductive strategy that has been frequently exploited across the animal kingdom. Mammalian embryonic diapause is categorized as obligate and facultative and broadly divided into three phases: entry into diapause, maintenance and termination of diapause. Obligate diapause occurs in every gestation of some species, while facultative diapause occurs in others, associated with metabolic stress, usually lactation. Embryonic diapause has been identified in over 100 animal species and the onset, maintenance and escape from diapause are regulated by cascades of environmental, hypophyseal, ovarian and uterine mechanisms that vary among species and between the obligate and facultative animal.
