Nearly one per cent of young women who have become pregnant claim to have done so as virgins, an American study has found.
Researchers interviewed 7,870 women aged 15 to 28 and found that more than 0.5 per cent of them who said they were virgins had also given birth - without the help of IVF.
The women were part of the long-running National Longitudinal Study of Adolescent Health, according to a report in the Christmas edition of the BMJ.
The girls were 12 to 18 years old when they entered the study in the 1994-95 school year and were interviewed periodically about their health and behaviour over 14 years.
Based on interviews with the women, 45 of the 5,340 pregnancies in this group through the years occurred in women who reported that they conceived without a man being involved.
Lead researcher Amy Herring and her colleagues devised an experiment where subjects were able to reply candidly to computer-generated self-interviews.
While the women weren't specifically asked about virgin births, the researchers used their replies to make a rough timeline of when the women started having sex and when they became pregnant.
The average age at which 'virgins' reportedly gave birth was 19.3 years.
Of the 45 women who became pregnant despite claiming to be virgins, 31 per cent said they had signed chastity pledges.
Only 15 per cent of non-virgins said they had signed a the pledge - promising to not have sex before marriage.
The 45 self-described virgins who reported having become pregnant (and the 36 who gave birth) were also more likely than non-virgins to say their parents never or rarely talked to them about sex and birth control.
About 28 per cent of the 'virgin' mothers' parents (who were also interviewed) indicated they didn't have enough knowledge to discuss sex and contraception with their daughters, and were less likely to know how to use condoms.
The researchers, from the University of North Carolina, say such scientifically impossible claims show researchers must use care in interpreting self-reported behaviour.
The researchers found that although the mothers in question were more likely to have boys than girls, and to be pregnant during the weeks leading up to Christmas, neither similarity to the Virgin Mary was statistically significant.
Virgin births in animals generally occur by asexual reproduction, and have been documented in multiple animals including pit vipers, boa constrictors, sharks, and Komodo dragons.
But Dr Herring said she knew of 'no medically-validated reports of virgin births in humans'.