Woman Gives Birth to Twins From Two Different Fathers

A 19-year-old just gave birth to twins — and they have different fathers. In an extremely rare case of “heteroparental superfecundation,” the Brazilian teenager’s babies are only half-siblings.

The girl, who hails from Minerios in Goias, claims she had sex with two different men on the same day. After performing a paternity test to see which man was the dad, she was shocked to see that only one baby matched the DNA.

“I remembered that I had had sex with another man and called him to take the test, which was positive,” said the shocked mother. “I didn’t know this could happen and the babies are very similar.”

The twins, born 16 months ago, are currently being raised by the mom and one of the fathers.

How Common Is Heteroparental Superfecundation?

Doctors are calling this a “one-in-a-million” case although some experts give different likelihoods of the occurrence.

The Guardian once reported how Jason Kasraie, the chair of the Association of Clinical Embryologists, scanned the scientific literature for other cases of heteroparental superfecundation. Citing two studies from decades ago, one author estimated that 1 in 400 pairs of fraternal twins actually come from different fathers. And another author estimated that 1 in 13,000 cases of paternity involve two men.

Heteroparental superfecundation occurs when a woman’s ovaries release two eggs in one menstrual cycle. Then, each egg needs to be fertilized by different men.

The process of releasing multiple eggs in one menstrual cycle is called hyperovulation. Studies have estimated that anywhere from 10% to 21% of women will experience hyperovulation in their lifetimes.

Interestingly, scientists have debated the idea of “sperm competition” for quite some time. Some hypothesize that sperm from two different men will fight with each other when they are together in the same vagina, with one set beating out the other in the end. While “kamikaze sperm” may indeed battle when in close quarters, we don’t know for sure how common that is. But what we do know is, sometimes they can live in peace—for 9 whole months.