Affecting millions of women in the U.S., pelvic organ prolapse is often chronic, beginning during the childbearing years and lasting for decades with urinary and fecal incontinence, and other unpleasant symptoms. Despite a bevy of treatment options, none are consistently effective at relieving symptoms for all women.

Each of these factors makes prolapse the “poster child” for the need for prevention, says Victoria Handa, who directs both the Department of Gynecology and Obstetrics at Johns Hopkins Bayview Medical Center and the Female Pelvic Medicine and Reconstructive Surgery Division.

However, she adds, there’s one glaring hitch: No one knows what causes pelvic organ prolapse in the first place, so no one knows how to stop it before it happens.

That’s why Handa and her colleagues have led an ongoing, National Institutes of Health-funded study since 2008 looking at what factors influence the risk of prolapse. The study has followed 1,500 women, each of whom has delivered at least one child. Participants represent all childbirth scenarios: planned cesarean, cesarean after labor began, cesarean in the second stage of labor, vaginal delivery without assisted extraction, vaginal delivery with forceps or a vacuum cup. Through physical exams and questionnaires to assess symptoms of pelvic floor disorders, Handa and her colleagues discovered that the primary factor that affects the risk of prolapse is a single vaginal delivery—with chances dramatically increased with the use of forceps or vacuum.

Wondering how vaginal delivery affects the pelvic muscles, Handa and her team also used a perineometer to assess volunteers’ pelvic muscle squeeze strength. For those who had had at least one vaginal delivery, squeeze strength was about 30 percent less than those who had never had a vaginal delivery. Those whose vaginal delivery involved forceps or a vacuum cup had squeezes 30 percent weaker still.

“This makes us think that pelvic muscles are an important key,” Handa says.

Most recently, the team invited volunteers to undergo 3D transperineal ultrasounds. Thus far, they’ve collected hundreds of videos that allow them to examine how the pelvic muscles look and behave when the volunteers contract them, bear down or perform other activities. Combined with other data the researchers have collected, these movies provide a wealth of anatomical information from every angle.

Eventually, Handa says, their work may lead to new treatments for prolapse—or, ideally, a way to prevent it altogether. “There are 4 million deliveries in the U.S. each year,” says Handa. “We see each of them as an opportunity to help women avoid this problem.”