Bi-paternal twins: it’s rare, but possible!
Did you know that roughly 3.5 out of every 1,000 children in the world are born a twin? That means 1 out of every 285 babies has a twin–either identical or fraternal. If you have already had a pair of fraternal twins, you are four times more likely to have another pair of twins. This is due to the fact that women who conceive fraternal twins tend to have a pattern of releasing multiple eggs at once. But there are types of twins that are even more rare! Only 1 out of 50,000 is ever born a conjoined twin, making it a VERY rare condition indeed. The most rare to date: bi-paternal twins.
Bi-paternal twins means that there are two children born at the same time, but with genetic material from two different fathers. To date, there have only been SEVEN cases of this type of twins.
The most recent comes from Vietnam, where in 2013, a woman gave birth to fraternal twins of the same sex, but with different types of hair: one has fine, straight hair, while the other has wavy, thick hair. The disparity in the appearances of the twins led the relatives of the parents to conduct a DNA test. It was discovered that the twins have different fathers, but it was confirmed that they had the same mother. The 34-year old father of one twin was not the father of the other.
To ensure there were no mistakes, the DNA test was conducted by the president of the Genetic Association of Vietnam. The results were backed up by the President of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists, who stated that there have been cases of bi-paternal twins in Australia.
Back in 2009, another women, Mia Washington, gave birth to a pair of twins who aren’t fully fraternal, but are only half-brothers. The twins–two boys–have two different fathers. The mother revealed that she had had an affair at the time when the twins were conceived, backing up the DNA results proving that there was a 99.9999% chance that her husband wasn’t the father of the other child.
But how does it happen? It all comes down to a basic understanding of the female reproductive system…
Most people think that women release just one egg every month when she ovulates. This is mostly true; however, it is not unheard of for a woman to release two eggs from her ovaries during ovulation. When this happens, both eggs remain viable for up to 24 hours. During this time, if there is sperm inside the woman’s body, that is how conception happens.
But what if there is sperm from TWO different males in her body? If the woman has had sex with two different men in the days leading up to ovulation, there is a chance that sperm from each man will fertilize the egg. Sperm can survive for as long as five days inside the woman’s reproductive system, so there is a chance that a woman can get pregnant even if she sleeps with two men a few days apart. The sperm from the two men will fertilize the eggs, leading to bi-paternal twins.
Of course, this is incredibly rare. The chances that a woman will release two viable eggs at once are fairly low, and the chance that the eggs will both be fertilized at the same time is also fairly slim. Considering most women won’t have unprotected sex with two different partners within such a short space of time, you can understand why bi-paternal twins truly are so rare!