The number of gender-affirming surgeries, intended to align patients’ physical appearance with their gender identity, nearly tripled in the United States between 2016 and 2019, according to a new analysis published in JAMA Network Open on Wednesday.

The number of procedures rose from about 4,550 in 2016 to about 13,000 in 2019, and then dipped slightly in 2020, according to the study’s estimates. Because of various data limitations, the researchers behind the study believe the true figures are higher.

Gender-affirming care has become a key political issue for conservatives in the run-up to the presidential election. At least 20 states led by Republicans have restricted or banned such care for minors.

Gender-affirming surgery is endorsed by a wide array of medical groups. Yet surprisingly little has been known about how often these operations are performed.

“There’s been a sense that more patients are asking about it, and ultimately pursuing it, but there wasn’t good data,” said Dr. Jason D. Wright, the chief of gynecologic oncology at Columbia University Vagelos College of Physicians and Surgeons, who led the research.

“Ours is one of the first studies to quantify the age groups and the procedures they’re undergoing.”

Past analyses have shown that such surgeries have been increasing. Health experts anticipated a sharper increase in recent years, in part because of changes in federal and state laws that often require coverage of transition-related care.

The Numbers: What kinds of procedures do patients opt for?

Dr. Wright and his colleagues drew patient counts from two databases maintained by the federal Agency for Healthcare Research and Quality in order to account for both inpatient and outpatient procedures, and weighted the figures to produce estimates for the entire country.

According to the analysis, about 48,000 patients underwent surgeries from 2016 through 2020. Breast and chest surgeries were the most common: There were about 27,187, or 56.6 percent of all gender-affirming surgeries.

Researchers estimated there were about 16,872 genital surgeries (35.1 percent of the total) during the period, and about 6,669 facial and cosmetic surgeries (13.9 percent).

Just over half of all patients were ages 19 to 30; about 22 percent were ages 31 to 40; and almost 8 percent were ages 12 to 18. The number of genital surgeries in particular increased with age, which researchers attributed to the higher complexity and “definitive nature” of the procedure.

The number of procedures overall rose from 2016 to 2019 but declined slightly in 2020, which the researchers said might have resulted from the onset of the Covid pandemic.

The data accounted only for surgeries in inpatient and ambulatory settings, and did not include cases in which surgeons omitted certain gender-related diagnosis codes. As a result, the study’s findings are “almost certainly under-captures” of the real figures, Dr. Wright said.

Background: Recent developments in gender-affirming care.

Much of the national discussion has centered on treatment for adolescents. Earlier this month, the American Academy of Pediatrics reaffirmed its guidelines regarding the gender-affirming treatment but also commissioned a fresh review of the research, after European health authorities found uncertain evidence for its effectiveness.