A pair of fraternal twins born in Vietnam have two different fathers, according to DNA tests. Known as heteropaternal superfecundation, the occurrence happens when a woman’s eggs are fertilized by two men within a very short period of time.
After noticing the twins did not seem to resemble each other, the father’s family requested DNA tests. The Genetic Association in Hanoi, Vietnam, performed the tests and verified, without question, that the twins have different fathers.
“There are only less than 10 known cases of twins with different fathers in the world. There might be other cases, but the parents and/or the twins were not aware of it or didn’t want to announce it,” said Le Dinh Luong, president of the Genetic Association.
According to the tests, a Y chromosome from one child did not match the man who thought he had fathered both twins. He is, however, the biological father of the other.
While the genetic tests proved the twins had different fathers, they also proved they have the same mother, confirming there was no accidental switch at the hospital. The two babies were born on the same day and are the same sex.
Local media reports the family is from Hoa Binh province and the children are now two years. One child has thick, wavy hair, while the other has hair that is thin and straight.
Due to a confidentiality agreement, Professor Luong declined to provide information about the clients, but stated that the local media reports detailing the twins’ names and location are incorrect.
“This is rare not only for Vietnam, but for the world,” noted Luong.
This is the only case of heteropaternal superfecundation ever reported in Vietnam.
Even though the possibility of twins being sired by two different men is a very uncommon event, it does happen on occasion. As previously reported by The Inquisitr, another case was reported in New Jersey last year.
When a woman, identified only as T.M., wanted child support from a man she claimed to be the father of her twins, the Passaic County Board of Social Services ordered a DNA test. The test revealed her eggs had been fertilized by two different males.
Judge Sohail Mohammed of the Passaic County Superior Court ruled that the man, identified as A.S., would only have to pay support for one child, not both. The mother admitted in court that she had been with another unnamed man the same week she had sex with A.S.
Health experts think these incidents may happen often, but are never detected.
“Normally, when a woman ovulates, she’s only producing one egg, but that’s not always the case,” fertility specialist Dr. Cynthia Austin told CBS News. “Sometimes there are two.”
Fraternal twins form when two sperms manage to fertilize two eggs. Sperm can stay active for several days in a woman’s body, so it is entirely plausible that sperm from two different fathers could inseminate two eggs. A woman is capable of becoming pregnant for five to seven days a cycle, so an egg fertilization from a different man can happen several days later.
“Sometimes it’s very obvious, if the father is one race and the babies are two different races,” Austin said. “I would say the vast majority of times, twins with different fathers, it goes unnoticed,” she said.
Identical twins can only be produced when a woman’s fertilized egg splits into two separate eggs very early in the pregnancy.
Since 2011, only seven cases of twins with different fathers have been reported throughout the world and fertility experts think there are probably many more. A review of paternity lawsuits published several years ago revealed that 2.4 percent of non-identical twins were fathered by two different males.
[Photo by China Photos/Getty Images]