Superfecundation
Superfecundation is the
fertilisation of two or more
ova from the same
cycle by
sperm from separate acts of
sexual intercourse. The term is also sometimes used to refer to the instances of two different males fathering
fraternal twins, though this is more accurately known as
heteropaternal superfecundation. This therefore leads to the possibility of twins also being half-siblings.
Superfecundation most commonly happens within hours or days of the first instance of fertilisation with ova released during the same cycle.
Ovulation is usually suspended during
pregnancy to prevent further ova becoming fertilised and to help increase the chances of a full term pregnancy. However, if an ovum is released after the female was already impregnated when previously ovulating, there is a chance of a second pregnancy -- albeit at a different stage of development. This is known as
superfetation.
Heteropaternal superfecundation is very rare in humans, though more common in other animals. This is primarily due to the predominance of 1:1 heterosexual partner pairings among humans. A woman who has sexual relations with two or more men at short intervals within the same ovulatory period can be impregnated by both men.
There have been noted examples in the past. The classic case, which is discussed in Williams Obstetrics (1980), was recorded in 1810 by John Archer, the first doctor to receive a medical degree in the United States. According to Archer, a white woman who had sex with a black man and a white man within a short time subsequently gave birth to twins--one white, one mulatto. Other cases have been reported since.
The term
superfecundation is derived from
fecund, meaning the ability to produce offspring.
*
Chimerism*
Heteropaternal Superfecundation*"
Is it possible for fraternal twins to have different fathers?" at
The Straight Dope*An example of heteropaternal superfecundation resulting from group sex can be found in the following journal article:
Lu et al (1994). "
Paternity Identification in Twins with Different Fathers".
Journal of Forensic Science July;
39(4), 1100-2.
