A new study has found that one in every 13 teenage girls, ages 14 to 20, reported having a group-sex experience, raising public health concern among the researchers involved.

Those who reported having had group sex were more likely to have been exposed to pornography and childhood sexual abuse than their peers, according to the study from the Boston University School of Public Health.

Emily Rothman, associate professor of community health sciences at BUSPH, and colleagues surveyed 328 females, who went to a Boston-area community or school-based health clinic, to see whether they ever had sex with multiple partners, whether consensual or forced.

Out of the 7.3 percent who said they had group sex more than half reported being pressured into it and 45 percent reported lack of condom use by a male during the most recent group sex encounter.

The study also found that participants who reported having group sex also were more likely to report cigarette smoking, dating violence victimization, or ever being diagnosed with a sexually transmitted disease.

While the majority of those who reported such activity said it was a one-time experience, 21 percent had multiple group-sex experiences and the average age of the first group sex experience was 15.6 years old.

The authors of the study said even if participation was voluntary, "it is crucial to know how this early experience shapes their sexual behavior trajectory and affects their lifetime risk for negative sexual, reproductive, and other health risk behaviors."

The authors said that while group sex among youth is an important public health topic it has “received very little attention to date.”

"It's time for parents, pediatricians, federal agencies, and community-based organizations to sit up, pay attention, and take notice: group sex is happening, and we need to be prepared to address it."