In the first broad demographic study of trends in gender-affirming surgeries in the United States, researchers found that the number of operations increased fourfold from 2000 to 2014. Some of the significant rise, according to a study published Wednesday in the journal JAMA Surgery, may be related to an increase in insurance coverage for the procedures.

“Early on we recognized there’s been a lot of work on health disparities having to do with age, race and so on that get collected in health-care settings,” said Brandyn Lau, an assistant professor of surgery and health sciences informatics at the Johns Hopkins University School of Medicine. “One of the things we need to know is whether [lesbian, gay and transgender] patients are getting the same care.”

Lau and other researchers from Johns Hopkins Medicine and Harvard University analyzed 15 years of data from the National Inpatient Sample, a collection of hospital inpatient information from across the country, and found a total of 4,118 gender-affirming surgeries.