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By Maggie Fox

Women may be having virgin births every day in the United States, according to new research published Tuesday.

Startled researchers found that about ½ of one percent of teens and young women interviewed as part of a larger survey reported they had given birth without ever having had sex.

“We thought, ‘This can’t be right. We must have done something incorrectly,’” says Amy Herring, a biostatician at The University of North Carolina at Chapel Hill who led the study.

Her team was looking at data for 7,870 women interviewed multiple times over 14 years, from their teen years to adulthood, as part of the U.S. National Longitudinal Study of Adolescent Health.

About 45 consistently stuck to a timeline that showed they had given birth before they ever had sex.

Herring thought it was an important issue, but also thought it might work for the BMJ (formerly British Medical Journal) Christmas issue, which publishes tongue-in-cheek medical studies. “We also thought it fit nicely with the Christmas theme,” Herring told NBC News.

Virgin birth is not unknown in nature. It’s known as parthenogenesis and it’s been documented in snakes, sharks, and Komodo dragons

But science has never demonstrated a human case of parthenogenesis. Herring thinks it may all be a mistake. “It’s self-reported pregnancy,” she says. And the survey, given by computer so the women and girls would feel free to answer questions honestly, didn’t follow up and ask them “Are you sure?” if they reported having had a baby yet not ever having had sex.

Social pressure could have made the women reluctant to admit they had sex before a certain age, or it could be they were confused about where babies come from, Herring says. About a third of the women who reported giving birth before they had sex for the first time said they had signed a virginity pledge, compared to 15 percent of all women who had babies.

“Parents were asked questions about how often they talked with their child about sex,” Herring adds. Those whose daughters reported virgin births were more likely to say sex was a difficult subject for them.

More of the women who had virgin pregnancies gave birth to boys than girls — 60 percent versus 40 percent. Herring isn’t sure what that might mean.

Could the girls have been mistaken about what counts as sex? “I think that’s possible,” Herring says. “I think that lots of people don’t know that the withdrawal method is subject to more failures than other birth control methods.” She points to a Canadian study that showed 10 percent of those students interviewed did not think that intercourse ending in orgasm counted as sex.

Then there were the virgin fathers. Yes, there were a few on the survey. Herring isn’t quite sure what to say about them.

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