Twins born in New Jersey were fathered by two different men, a judge has declared, after a court-ordered DNA test showed that the man identified in a paternity suit was the parent of only one of the girls.
Acknowledging that the case would provoke “sheer disbelief”, Judge Sohail Mohammed said the paternity test was accurate and that the conception of the twins by two separate fathers was part of a rare but growing phenomenon of “bi-paternal twins”.
The mother of the twins, who are now two years old, had told the board of social services in Passaic County, northern New Jersey, that a former lover was the father of her twin girls. The board duly filed a child-support suit on her behalf last October, which referred to the mother only as TM and to their reputed father as AS.
A DNA test then showed that she was half correct: AS had fathered only one of the girls. Confronted with the finding, “the mother testified that within about a week, she had sexual intercourse with two men, AS and another man”, the judgment, filed this week, said.
The other man has not yet been identified, nor has he undergone a DNA test, the judge said. Such a thing had never been seen by a court in New Jersey, he added, although cases involving bi-paternal twins have been heard in Colorado and New York.
Jackson Kirkman-Brown, a reader in reproductive biology at the University of Birmingham, said that two separate sperm fertilised two separate eggs every time a woman conceived non-identical twins.
“Having two eggs and two sperm is no rarer than having non-identical twins, by definition,” he said. “The fact that the woman had sex with two different men to get that set of non-identical twins is far rarer.”
He said that the mother “will have ovulated two eggs — that could be two from one ovary or one from each. Then the question just becomes what sperm finds the eggs. If she had sex with two men in the 36 hours prior to that, there may be sperm from both of those men inside the female reproductive tracts.”
Sperm have been found to survive for up to a week in the female reproductive tracts, although this is extremely rare, he said.
“Sperm will survive in the female tract for up to a few days. Theoretically she has probably got a three or four-day window for that sperm to survive — usually they don’t survive a lot longer than that.”
In New Jersey, Karl-Hans Wurzinger, of the American laboratory testing company LabCorp, told the court that his laboratories encountered about six cases a year.
Judge Mohammed said that the incidence of bi-paternal twins had risen because of modern fertility treatments as well as increased “promiscuity and other factors”. He ordered the father AS to pay $28 a week in support of the twin identified as his daughter.
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