They are extremely rare and very little known cases, at least publicly, but it is possible that two twins each have a different father, even if they are begotten at the same time by the same mother. This is the case of some Vietnamese twins who, seeing them differently, the family subjected them to a DNA test to verify their identity. According to the results, it was proven to 99% that one of the twins was not the son of the woman's husband.
This phenomenon that gives rise to twins of different parents it is known as heteroparental multiple fertilization or heteroparental superfecundation, which happens when a woman's eggs are fertilized by more than one man within a short period of time.
Superfetation
But how is it possible? Have you become pregnant with one man while previously pregnant with another? That's right, it's called superfetation. It is not usual but it can happen that the woman releases more than one egg in a single period of ovulation. Typically, when conception occurs, the woman's reproductive system stops producing eggs. Only very rarely can the menstrual cycle be repeated and a new egg is released while an embryo already exists. Even weirder is that this egg is also fertilized: then superfetation occurs, when they come together two embryos of different gestational ages.
In addition to superfetation this mother has been added heteroparentality, that is, to get pregnant with two different men. She has had an ovulation in which at least two ovules have occurred, and each has been fertilized by a different man in a few days.
Heteroparental multiple fertilization
The heteroparental multiple fertilization It occurs when two ovules are fertilized by two sperm from two different men. To make it clearer, the woman releases an egg, has sex with a man and one of her sperm fertilizes the woman's egg. In the same cycle he returns to ovulate, has sexual relations with another man and one of his sperm fertilizes the second ovum of the woman giving rise to a pregnancy of twins of different parents who share the maternal uterus.
It is a rare situation that only occurs in one of every 13,000 fertilizations, to which we must take into account that women must have sexual relations with different men in a maximum term of 5 days.
"There are only less than 10 known cases of twins from different parents in the world. There may be other cases, but the parents and / or twins were not aware of it or do not want to report it," said Professor Dinh Le Luong, president of the Vietnam Association of genetics based in Hanoi, which did the DNA test.
