Embryonic diapause (from late 19th century English: dia- ‘through’ + pause- 'delay') (aka delayed implantation in mammals) is an evolutionary reproductive strategy used by several animal species across a number of kingdoms, including approximately 130 different mammals, which takes place in order to ensure the survival of offspring. The process occurs at the blastocyst stage of embryo development in most species, and is characterized by a dramatic reduction or complete cessation of mitotic activity, arresting most often in the G0 or G1 phase of division. In placental embryonic diapause, the embryonic blastocyst does not immediately implant in the uterus after sexual reproduction has created the zygote, but rather remains in this non-dividing state of dormancy until conditions allow for attachment to the uterine wall to proceed as normal. As a result, the normal gestation period is extended for a species-specific time. Organisms which undergo embryonic diapause are able to synchronize the birth of all offspring to the most favorable conditions for reproductive success, irrespective of when mating took place. As timing and environment are important, many different factors can induce embryonic diapause, such as the time of year, temperature, lactation and supply of food. Embryonic diapause is considered a relatively widespread phenomenon outside of mammals, with known presence in the reproductive cycles in many insects, nematodes, fish, and other non-mammalian vertebrates. It has been observed additionally in less than 2% of mammalian species, including certain rodents, bears, armadillos, mustelids (e.g. weasels and badgers), and marsupials (e.g. kangaroos). Some groups only have one species that undergoes embryonic diapause, such as the roe deer in the order Artiodactyla. Furthermore, recent studies have demonstrated even the ability for species which do not traditionally undergo embryonic discontinuous development to exhibit reversible developmental arrest, indicating some potential evolutionary significance of this phenomenon, or at least some evidence that embryonic diapause is more widespread than we currently understand. General mechanism All multicellular organisms, from their conception, begin as a small number of cells and only grow and develop as those cells divide. In organisms which are capable of embryonic diapause, in non-ideal reproductive conditions, there is a cessation of cellular division which prevents the embryo from growing and maturing, delaying the maturation of the embryo until conditions are ideal enough to promote the survival of the offspring, and in some cases, the mother. Regulation of the cell cycle as it relates to embryonic diapause has been