Female genital mutilation was criminalized in the U.S. more than 20 years ago, but the first major criminal prosecution related to the procedure is only unfolding now. Dr. Jumana Nagarwala will appear Tuesday in federal court in Michigan for a hearing related to her bail conditions. Seven additional defendants — including another doctor — have been charged with assisting Nagarwala, a U.S.-educated emergency physician, in a 12-year conspiracy to cut the genitals of prepubescent girls as part of a religious ritual.

The case is shedding light on a procedure that remains little understood in the U.S. — in part because we don’t know how widely it’s practiced. Female genital mutilation (also known as female genital cutting or female circumcision) is an umbrella term for the ritual, medically unnecessary excision of part or all of a girl’s external genitalia. It can refer to several different types of cuts, all which are associated with negative health consequences — including difficulty urinating, reduced sexual pleasure, serious infections and complications in childbirth — and it is recognized by international groups like the World Health Organization as a human rights violation. The practice is justified for a variety of reasons, including religion, cleanliness, preservation of virginity by reducing sexual desire or as rite of passage to womanhood.

Female genital cutting has been documented in communities across Africa, the Middle East and Asia, including among the Dawoodi Bohras, the Indian Shiite Muslim sect to which Nagarwala belongs. The WHO estimates that more than 200 million girls and women have undergone the practice in the places where it’s common, and more than 3 million girls are at risk of the procedure each year. But the global data on female genital mutilation is incomplete: There has been research on the practice in Africa, where it’s believed to be most common, since the late 1980s, but other countries like Indonesia have only recently begun to investigate it via surveys.

This is problematic for the U.S., which made the genital cutting of female minors illegal in 1996 but doesn’t conduct its own surveys on the procedure’s prevalence. Collecting the data is difficult, and the issue hasn’t historically been a public health priority in the U.S. Instead, government agencies like the Centers for Disease Control and Prevention rely on data collected abroad and immigration rates from countries where the practice is common to estimate the number of women and girls who may be at risk. The lack of data means that advocates and government agencies don’t know where prevention resources are needed, clinicians don’t know which patient populations are most at risk or which kinds of cutting are most prevalent, and the problem continues to be perceived as one that primarily affects other countries.

The most recent U.S. estimate — which doesn’t even try to quantify the number of women and girls who have undergone the procedure — concluded that as of 2012, there were approximately 513,000 women and girls at risk of genital mutilation — more than three times higher than estimates from 1990. But that number should be taken with a big grain of salt, according to CDC epidemiologist Thomas Clark. For example, the data doesn’t account for immigrants from countries where female genital cutting isn’t studied or widely practiced. That means, for example, that the Dawoodi Bohra aren’t part of the estimate; even though female genital cutting appears to be widely practiced in their community, the Bohras make up a very small part of the Indian population, so India isn’t one of the countries in the estimate.

“You also can’t assume that people who come to the U.S. are a representative sample of their country of origin,” Clark said. That’s especially problematic for estimating rates of female genital cutting, since it’s not practiced uniformly within countries. It’s also possible, he said, that some immigrants abandon the procedure as they assimilate. Awareness that the practice is illegal in the U.S. may be an additional deterrent, although it’s also illegal in many African countries.

And some advocates point out that although the estimates focus on immigrants, it’s important to acknowledge that female genital cutting isn’t new to the U.S. Female circumcision was performed as a treatment for masturbation by American physicians as recently as the mid-20th century; to bring attention to this history, a white woman from Minnesota named Renee Bergstrom wrote an essay in the Guardian about the removal of her clitoris by a Christian doctor in a church clinic when she was a young girl.

“This isn’t just a problem that immigrants are bringing here,” said Shelby Quast, the director of the Americas office of Equality Now, a global nonprofit focusing on women’s rights.

Without accurate data, it’s hard to launch prevention efforts or provide resources to affected women and girls. But gathering information about a secretive procedure believed to be concentrated among tightly knit immigrant communities remains difficult. That problem is compounded by the fact that although cutting is practiced by a number of different religious groups, Muslims like Mariya Taher — the co-founder of Sahiyo, a Bohra anti-cutting group — have said they have been reluctant to to speak out because they worry that openly discussing the practice may encourage anti-Islam legislation and rhetoric. (Female genital mutilation has no scriptural basis in either Islam or Christianity.)

Ghada Khan, a Ph.D. student and researcher at George Washington University who is currently conducting qualitative research on female genital cutting in the Washington, D.C., area, said she’s received pushback from Muslim community members with such concerns. It’s not an unjustified fear: In response to Nagarwala’s arrest, a Michigan lawmaker introduced a bill that would ban residents from using Sharia law in state courts.

But Khan thinks that better data collection could actually help combat the idea that female genital cutting is a Muslim ritual by showing that it’s practiced across religious and ethnic boundaries. “People say it’s a religious practice, but all of their justifications are cultural — it’s fundamentally about controlling a woman’s sexuality,” she said. “It’s easier to recognize that when you see how many different groups are practicing it, from many different parts of the world.”

Although research on the practice has become more of a U.S. priority in recent years, there aren’t many good ways of obtaining information about its prevalence. Because the number of women and girls at risk in the U.S. is small within the context of the millions of women and girls in the country overall, adding questions about female cutting to population-wide health surveys — which draw from small samples — wouldn’t give researchers a good sense of how common it is, according to Clark.

Another option would be to conduct targeted surveys in immigrant groups where prevalence might be high. These wouldn’t provide a comprehensive snapshot of how common the procedure is overall, but it would offer researchers and clinicians more information about communities’ perspectives on it and whether people are continuing to engage in the ritual after moving to the U.S., Clark said. That, in turn, would make it easier to target resources to addressing the issue — and help health care providers identify the cuts their patients have been subjected to.

Such efforts would also be an important complement to litigation like the Nagarwala case, according to Taher. “We need to make sure people are being held legally accountable, but the law alone can’t change community perceptions or help victims heal,” she said.