Conversely, those who were sexually active before taking the pledge frequently deny their sexual history, according to study findings published in the American Journal of Public Health.
These findings imply that virginity pledgers often provide unreliable information, making assessment of abstinence-based sex education programmes unreliable.
In addition, these teens may underestimate their risk of exposure to sexually transmitted diseases.
"Teenagers do not report their past sexual activity accurately, with virginity pledgers giving more inaccurate reports of their past sexual activity," study author Janet Rosenbaum, of Harvard University in Cambridge, Massachusetts, said on Friday.
Rosenbaum said that in the future, such studies should focus on more reliable collected data such as medical sexually transmitted disease (STD) tests.
Previous research shows that survey respondents tend to answer questions about sexual activity according to their current beliefs, particularly if their current attitudes conflict with their past behaviours.
Survey respondents may also underreport or overreport their health risk behaviour.
Rosenbaum evaluated retractions of virginity pledges and reports of sexual histories among a nationally representative sample of 12- to 18-year-olds who took part in the national longitudinal study of adolescent health.
"People's memories of their behaviour are consistent with their beliefs rather than their actual behaviour"
Janet Rosenbaum, study author
The students were first interviewed in 1995 and followed up in 1996.
In the first survey, about 13% of adolescents reported that they had taken a pledge of virginity. One year later, however, more than half of this group said they had never taken such a pledge, Rosenbaum said.
In addition, more than one in 10 students who reported being sexually active in 1995 said they were virgins in 1996.
Students who reported they were sexually active in the second survey were more than three times as likely as their peers to deny they had taken a pledge of virginity.
The adolescents' denials of virginity pledges and sexual histories were associated with changes in their sexual and religious identities, the report indicates.
Adolescents who abandoned a born-again Christian identity were more than twice as likely as their peers to say they had never taken a virginity pledge.
"If those who deny their sexual pasts perceive their new history as correct, they will underestimate the sexually transmitted disease risk"
Janet Rosenbaum, study author
On the other hand, 28% of nonvirgins who later took a virginity pledge retracted their sexual histories during the 1996 survey. The same was true of 18% of nonvirgins who later adopted a born-again Christian identity.
Sexually active teens who later took virginity pledges were four times as likely to deny previous reports of sexual activity than were those who had not taken virginity pledges.
Rosenbaum said it was impossible to know why pledgers retracted their sexual history because it was impossible to know whether respondents actually had sex.
"Psychology studies in a variety of contexts seem to demonstrate that people's memories of their behaviour are consistent with their beliefs rather than their actual behaviour," she added.
This, however, could cause problems for health workers trying to halt the spread of STDs amongst the young.
"If those who deny their sexual pasts perceive their new history as correct, they will underestimate the sexually transmitted disease risk stemming from their pre-pledge sexual behaviour," Rosenbaum said.