Nine months after having sex with two different men on the same day, the 19-year-old woman gave birth to this "one-in-a-million" set of twins.
As her twins’ first birthday drew closer, a Brazilian mother began to have doubts about the identity of the children’s biological father. Nine months before they were born, she’d had sex with two different men on the same day, and she wasn’t entirely sure which of the men had fathered the infants.
To confirm her suspicions, the New York Post reported, she took a paternity test, but the results weren’t quite what she’d expected. They came back as a match — for just one of the twins.
“I remembered that I had had sex with another man and called him to take the test, which was positive,” the new mother, who asked to remain anonymous, told local news outlets. “I was surprised by the results. I didn’t know this could happen, and the babies are very similar.”
Evidently, this sort of thing can happen, though it is incredibly rare.
“It is possible to happen when two eggs from the same mother are fertilized by different men,” Dr. Tulio Jorge Franco, the woman’s attending physician, said. “The babies share the mother’s genetic material, but they grow in different placentas.”
The technical term is “heteropaternal superfecundation,” but to put it simply, the extremely rare phenomenon occurs when two eggs are released during the same menstrual cycle. When this happens, it’s possible that each ovum could be fertilized by sperm cells during two separate acts of sexual intercourse. In this instance, the second egg was fertilized by a different man than the first.
Franco described the phenomenon as “one in a million” and said he believed there are only about 20 other instances of the same thing happening in the world. Other doctors, however, estimate that there are around 400 existing cases.
Per Firstpost, heteropaternal superfecundation occurs more commonly in other animals like cows, dogs, and cats as a tactic employed by females to intentionally boost their chances of conceiving multiple offspring.
This is not a necessity for humans, however, hence the rarity of the bizarre phenomenon.
A similar situation happened back in 2015, as well, when a father in New Jersey was told he only had to pay child support for one of two twin girls — because she was the only one he technically fathered.
According to CNN, the mother had testified that within a week’s time, she’d had sex with two different men. She took the man she believed to be both girls’ father to court seeking child support, but DNA testing only matched him to one of the girls.
“This is a case of first impression in New Jersey, and only a handful of reported cases exist nationwide,” Superior Court Judge Sohail Mohammed said when he made his ruling.
The ruling also cited a 1997 article written by DNA expert Karl-Hanz Wurzinger. In his article, Wurzinger wrote that one in every 13,000 reported paternity cases involving twins had different fathers.
Given that the lifespan of a sperm is between seven and 10 days, Keith Eddleman, director of obstetrics at Mount Sinai Hospital in New York, explained at the time, there was enough room for overlap when the woman’s menstrual cycle released two separate ova, allowing both men’s sperm to fertilize the eggs separately.
In some cases, Eddleman said, a woman can give birth to twins of different races, which would likely be more obvious to the parents as well.
“It is more common than we think,” Eddleman said. “In many situations, you would never know because there is no reason to do a paternity test on [both] twins.”