The mother testified in a paternity case that, within a week's time, she had sexual intercourse with two men -- the man genetic tests confirmed as the father and another unidentified man.
The judge acknowledged the unusual circumstances of the case in a ruling this week.
"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 in his ruling.
The mother of 2-year-old twins went to court seeking child support from the father of the child. Neither party is named in court documents.
The Passaic County Board of Social Services filed an application to establish paternity and child support on behalf of the mother. A DNA test established that the man is not the father of one twin, according to the ruling.
Given that the mother provided the name of only one man, a paternity test was performed on that man, the documents said.
The ruling cited a 1997 article published by DNA expert Dr. Karl-Hanz Wurzinger that said one in every 13,000 reported paternity cases involving twins have different fathers.
Twins with different fathers are considered a rare phenomenon by the scientific community, according to the ruling.
Dr. Keith Eddleman, director of obstetrics at Mount Sinai Hospital in New York, said the process in which two ova are fertilized within the same menstrual cycle by two separate sperm is called superfecundation. Twins with different fathers are called bipaternal or heteropaternal twins, Eddleman said.
Since an egg has a life span of 12 to 48 hours and a sperm is viable for seven to 10 days, there is about a week's time for potential overlap and the fertilization of two eggs by two sperm from two separate acts of intercourse with different men, according to Eddleman.
"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 twins."
He believes the increase in the number of cases of bipaternal twins is a result of technological advances and the ability to detect it more easily.
The medical textbook example of bipaternal twins involves twins of different races, according to Eddleman.
There appears to be no central registry that documents cases of bipaternal twins, but some in the medical community believe it happens more frequently now than 50 years ago as a result of promiscuity, reproductive technologies, ovulation induction, and other factors, Mohammed said in his ruling.
Mohammed ordered the father to pay $28 a week in child support for the child, the ruling said.
CNN was not immediately able to reach the attorney for the Passaic Board of Social Services, which brought the case to court.