Superfetation
Superfetation (also spelled superfoetation and superfœtation – see fetus) is the simultaneous occurrence of more than one stage of developing offspring in the same animal.[1] It is not believed that it occurs naturally in humans.[2]
In mammals, it manifests as the formation of an embryo from a different estrous cycle while another embryo or fetus is already present in the uterus. When two separate instances of fertilisation occur during the same menstrual cycle, it is known as superfecundation.
Superfetation is claimed to be common in some species of animals. In mammals, it can occur only where there are two uteri, or where the estrous cycle continues through pregnancy.
Other animals
Animals that have been claimed to be subject to superfetation include rodents (mice and rats), rabbits, horse, sheep, marsupials (kangaroos and sugar gliders), felines, and primates (humans). Superfetation has also been clearly demonstrated and is normal for some species of poeciliid fishes.[3]
Humans
While proposed cases of superfetation have been reported in humans, the existence of this phenomena in humans is deemed unlikely.[2] Better explanations include differential growth between twins due to various reasons such as twin-to-twin transfusion syndrome.[2] Artificially induced superfetation has been demonstrated, although only up to a short period after insemination.[2]
References
- ^ Roellig, K; Menzies, BR; Hildebrandt, TB; Goeritz, F (February 2011). "The concept of superfetation: a critical review on a 'myth' in mammalian reproduction". Biological reviews of the Cambridge Philosophical Society. 86 (1): 77–95. doi:10.1111/j.1469-185X.2010.00135.x. PMID 20394608.
- ^ a b c d McNamara, HC; Kane, SC; Craig, JM; Short, RV; Umstad, MP (February 2016). "A review of the mechanisms and evidence for typical and atypical twinning". American Journal of Obstetrics and Gynecology. 214 (2): 172–191. doi:10.1016/j.ajog.2015.10.930. PMID 26548710.
- ^ FishBase's glossary
External links
- Superfetation in Beef Cattle Doctoral Thesis; Joel Andrew Carter, Louisiana State University, Defended 2002-03-18
- Superfetation in fish