For more than 3.3 million girls and women in the United States, the first time they had sex was involuntary and traumatic, according to a new study.

"A practicing physician is likely to see several patients each week who have experienced this form of trauma," wrote the authors of a study published this week in JAMA Internal Medicine, a medical journal.

The authors noted that "the #MeToo movement has highlighted how frequently women experience sexual violence," but "no recent studies have assessed the prevalence of forced sex during girls' and women's first sexual encounter or its health consequences."

Fifty percent of the girls and women who reported forced sexual initiation said they were coerced by someone larger or older. More than half described being pressured verbally, and 46% said they were held down.

Females also reported being drugged (22%), threatened physically (26%) or harmed physically (25%).

The common thread of a perpetrator was gender, with slight differences for socioeconomic or racial characteristics.

"Forced sexual initiation was reported by women of all racial and ethnic groups and varied modestly by poverty status, level of educational attainment, or place of birth," the study reported.

Compared with women who voluntarily consented to sex the first time, women who were forced were less likely to be white, somewhat more likely to be born outside the United States, more likely to have incomes below the poverty level and less likely to be college educated.

"However, as presented in these data, all demographic groups reported substantial rates of forced sexual initiation," emphasized the authors, from Cambridge Health Alliance and Harvard Medical School in Massachusetts, and City University of New York.

The average age of females forced into sex was 15, and the average age of perpetrators was 27, according to the study of 13,310 women ages 18 to 44 years.

However, nearly 7% of the study sample who reported being forced were younger than 10 years old. That compared with 0.1% of girls who said the first time they had sex was voluntary.

Girls and women who were forced the first time they had sex "had elevated rates of subsequent adverse reproductive, gynecologic, general health, and functional outcomes." They also experienced increased risk of repeated sexual victimization later in life, the study's authors wrote. In addition, they were more likely to have an unwanted first pregnancy and abortion.