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Superfecundation is the fertilization of two or more ova from the same cycle by sperm from different sources, which can occur from separate acts of sexual intercourse or a single act involving multiple sperm donors (e.g., double penetration). This can result in twin babies with different biological fathers.[1][2]
The term superfecundation is derived fromfecund, meaning able to produce offspring.Homopaternal superfecundation is fertilization of two separate ova from the same father, leading tofraternal twins,[3] whileheteropaternal superfecundation is a form of atypical twinning where, genetically, the twins are half siblings – sharing the same mother, but with different fathers.
Sperm cells can live inside a female's body for up to five days, and once ovulation occurs, the egg remains viable for 12–48 hours before it begins to disintegrate.[4] Superfecundation most commonly happens within hours or days of the first instance of fertilization with ova released during the same cycle.
Ovulation is normally suspended duringpregnancy to prevent further ova becoming fertilized and to help increase the chances of a full-term pregnancy. However, if an ovum is atypically released after the female was already impregnated when previously ovulating, a chance of a second pregnancy occurs, albeit at a different stage of development. This is known assuperfetation.[5]
Heteropaternal superfecundation is common in animals such as cats and dogs. Stray dogs can produce litters in which every puppy has a different sire. Though rare in humans, cases have been documented. In one study on humans, the frequency was 2.4% amongdizygotic twins whose parents had been involved inpaternity suits.[6]
In 1982, twins who were born with two different skin colors were discovered to be conceived as a result of heteropaternal superfecundation.[5][7]
In 1995, a young woman gave birth todiamnioticmonochorionic twins, who were originally assumed to be monozygotic twins until a paternity suit led to a DNA test. This led to the discovery that the twins had different fathers.[3]
In 2001, a case of spontaneous monopaternal superfecundation was reported after a woman undergoing IVF treatments gave birth to quintuplets after only two embryos were implanted.Genetic testing supported that the twinning was not a result of the embryos splitting, and that all five boys shared the same father.[5][8]
In 2008, on theMaury Show a paternity test on live television established a heteropaternal superfecundation.[9]
In 2015, a judge inNew Jersey ruled that a man should only pay child support for one of two twins, as he was only the biological father to one of the children.[10]
In 2017, an IVF-implanted surrogate mother gave birth to two children: one genetically unrelated child from an implanted embryo, and a biological child from her own egg and her husband's sperm.[11]
In 2019, a Chinese woman was reported to have two babies from different fathers, one of whom was her husband and the other was a man having a secret affair with her during the same time.[12]
In 2022, a 19-year-old Brazilian fromMineiros gave birth to twins from two different fathers with whom she had sex on the same day.[13]
Greek mythology holds many cases of superfecundation:
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