Many women say 1st sexual experience was forced in teens, new study finds

As the #MeToo era continues to unfold, a new study shows how often the first sexual experience for women is forced or coerced.

One in 16 women reported experiencing forced sexual initiation, usually in their teen years and usually with someone a few years older, according to research published Monday in the Journal of the American Medical Association (JAMA).

When expanded nationwide, that number totals more than three million women in the U.S., according to the study.

The study’s authors described the experience of forced sexual initiation as rape.

"This data represents reported experiences, which means there many, many more [women] who have also had this experience who may not feel they could disclose it," sexual education expert Elizabeth Schroeder, who was not involved with the study, told "Good Morning America." "My guess is the number is much higher."

The study found that women who were forced to have sex during their first sexual encounter were more likely to be younger in age (approximately two years) than women who engaged in consensual intercourse.

Researchers who conducted the study also found that instances of forced sexual experiences led to lasting health and economic repercussions for many of the women.

Compared with women whose first sexual experience was voluntary, women with forced sexual initiation were more likely to experience an unwanted first pregnancy or an abortion, endometriosis, pelvic inflammatory disease and problems with ovulation or menstruation, according to the study.

Survivors of forced sexual initiation also more frequently reported illicit drug use, resided below the poverty line and had lower levels of education than women who engaged in consensual intercourse, the study said.

The study's researchers based their data on a sample of more than 13,000 women between the ages of 18 and 44.

The Rape, Abuse & Incest National Network (RAINN), an anti-sexual violence organization, defines consent as "an agreement between participants to engage in sexual activity."

The organization emphasizes that consent "should happen every time," saying, "Giving consent for one activity, one time, does not mean giving consent for increased or recurring sexual contact."

Consent is something people learn about when they're very young, but the lessons of it often fall aside in later years, according to Schroeder.

"Such messages as 'hands are not for hitting' and 'hands on your own body' are repeated throughout children’s formative years," she said. "The problem is, we stopped teaching those lessons and then failed to connect them to romantic and sexual relationships as kids get older."

Some states are adding information about healthy relationships and consent to their sex education curriculum.

In May, Colorado became the ninth state in the U.S. to require teaching about consent as part of sex education in K-12 schools.

"I wholeheartedly believe we should be teaching more about consent, but at the same time can’t expect that having a few class sessions on consent are sufficient to counteract the toxic masculinity that is pervasive in and valued by the dominant power structure in the US," said Schroeder.

Other experts hope they are seeing a sea change as young people, particularly boys, grow up with different expectations of sexual encounters.

Dr. Harold Koplewicz, a psychiatrist and president of the Child Mind Institute in New York City, told ABC News last year he believes "there's a very big difference between young men who are between 18 and 22 and older men who, let's say, are above 40 years of age. A lot of these guys have grown up with a different sensibility."

"Part of growing up is learning to make informed choices, not to give in to impulsivity," Koplewicz said. "Becoming a man means learning to think about people other than yourself right now -- including how you’ll feel in the future."

Dr. Sejal Parekh, a pediatrician and a member of the ABC News Medical Unit, contributed to this report.