Superfetation (also spelt superfoetation, based on a false etymology — see fetus) is the formation of a fetus while another fetus is already present in the uterus. When there are two separate instances of fertilisation during the same cycle, rather than different cycles, it is known as superfecundation. In historical linguistics, etymology is the study of the origins of words. ... Fetus at eight weeks A fetus (alternatively foetus or fÅ“tus) is an unborn human offspring from the end of the 8th week of pregnancy (when the major structures have formed) until birth. ... Female internal reproductive anatomy The uterus or womb is the major female reproductive organ of most mammals, including humans. ... A sperm attempting to fertilize an egg Fertilisation (also known as fertilization and syngamy) is fusion of gametes to form a new organism. ... The phrase menstrual cycle ( or period) refers to the recurring physiological changes in a females body that are under the control of the reproductive hormone system and necessary for reproduction. ... Superfecundation is the fertilisation of two or more ova from the same cycle by sperm from separate acts of sexual intercourse. ...

It is claimed to be common in some species of animals, but is extremely rare in humans. It can only occur where there are two uteri, or where the menstrual cycle continues through pregnancy. Animals which have been claimed to be subject to superfetation include rodents (mice & rats) farm animals (horses & sheep) and primates (monkeys and man). The phrase menstrual cycle ( or period) refers to the recurring physiological changes in a females body that are under the control of the reproductive hormone system and necessary for reproduction. ... A pregnant woman Human pregnancy is the part of the life reproduction process in which a human female carries a live offspring from implantation until childbirth. ... Families Many, see text The order Rodentia is the most numerous of all the branches on the mammal family tree. ... Feral mouse Feral mouse A mouse is a mammal that belongs to one of numerous species of small rodents in the genus Mus and various related genera of the family Muridæ (Old World Mice). ... Species 50 species; see text *Several subfamilies of Muroids include animals called rats. ... Binomial name Equus caballus Linnaeus, 1758 The Horse (Equus caballus) is a sizeable ungulate mammal, one of the seven modern species of the genus Equus. ... Binomial name Ovis aries Linnaeus, 1758 A sheep is any of several woolly ruminant quadrupeds, but most commonly the Domestic Sheep (Ovis aries), which probably descends from the wild moufflon of south-central and south-west Asia. ... Families 13, See classification A primate is any member of the biological order Primates, the group that contains all lemurs, monkeys, apes, and humans. ... Cynomolgus Monkey at Batu Caves, Malaysia Monkeys, Mori Sosen (1749-1821) A monkey is any member of two of the three groupings of simian primates. ... Image of a man on the Pioneer plaque sent to outer space A man is a male human adult, in contrast to an adult female, which is a woman. ...

Reports of superfetation occurring long after the first impregnation have often been treated with suspicion and some have been clearly discredited. Other explanations have been given (and demonstrated) for different levels of development between twins. Artificially induced superfetation has, however, been demonstrated although only up to a short period after insemination. Superfetation has also been clearly demonstrated in poeciliidae fish [1]. Genera Alfaro Belonesox Brachyrhapis Cnesterodon Gambusia (mosquitofishes) Girardichthys Girardinus Heterandria Heterophallus Jenynsia Limia Micropoecilia Phallichthys Phalloceros Phalloptychus Platypoecilus Poecilia (mollies) Poeciliopsis Priapella Pseudoxiphophorus Quitana Xiphophorus (swordtails, platys) Poeciliidae is a family of fresh-water fishes, which are ovo-viviparous (they give birth to live young; see also live-bearing aquarium... Groups Conodonta Hyperoartia Petromyzontidae (lampreys) Pteraspidomorphi (early jawless fish) Thelodonti Anaspida Cephalaspidomorphi (early jawless fish) Galeaspida Pituriaspida Osteostraci Gnathostomata (jawed vertebrates) Placodermi Chondrichthyes (cartilaginous fish) Acanthodii Osteichthyes (bony fish) Actinopterygii (ray-finned fish) Sarcopterygii (lobe-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) A fish is a poikilothermic (cold-blooded)* water-dwelling...

Flavia D'Angelo, an Italian woman claiming to have become pregnant with triplets three months after initially getting pregnant, caused global media interest in 2001 (BBC News). However, it was later revealed to be a hoax (BBC News).

External links

• Superfetation in Beef Cattle Cattle Doctoral Thesis; Joel Andrew Carter, Louisiana State University, Defended 2002-03-18
• Superfetation in fish
• A case of twins with probable superfetation a report of a case of superfetation demonstrated through different paternity of twins.