The Grapevine

NJ Twins Have Different Fathers Due To Rare, But Not Impossible, 'Superfecundation'

twins
Two sperm from two different men, within the same week, led to one woman with twin daughters with different dads. Donnie Ray Jones, CC BY 2.0

On Monday, a New Jersey judge ruled in favor of a woman seeking child support from the father of one of her twins — the result of a medical rarity known as “superfecundation,” in which sperm from two partners fertilize two eggs from the same menstrual cycle.

In making his decision, Passaic County Superior Court Judge Sohail Mohammad leaned on past evidence that superfecundation has real scientific basis, such as a 1992 study that found the phenomenon can explain roughly two percent of paternity cases. The woman will receive $28 a week from the new father, who the woman suspected fathered one of her daughters but not the other.

In most circumstances of twin births, one of two things happens. Either one sperm fertilizes one egg and it splits, producing two identical twins, or two different sperm fertilize two eggs, producing fraternal twins. In rare cases, parents will end up with so-called polar body twins, who share 75 percent of their genes. This occurs when an egg divides randomly during ovulation and gets fertilized by two different sperm.

Superfecundation occurs when a woman has intercourse with two or more men within the same menstrual cycle. In her testimony to the court, the woman admitted she had had sex with two different men within a week. A DNA test showed the man suspected of being the father was only responsible for conceiving one of the children.

Speaking to The New York Times, Dr. Jennifer Wu, an OBGYN at Lenox Hill Hospital in New York, pointed to assistive reproductive technologies as a partial cause of a new trend, particularly as gay men both contribute sperm to a pregnancy. “That’s why we’re seeing it more often than we were in the past,” she said, “when we were relying on nature and women who have more than one sexual partner in the same cycle around the time of ovulation.”

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