A new study from the American Medical Association indicates that the number of metropolitan areas in which there’s little choice of health care insurers is growing.

Healthcare Finance News reports that the 2017 edition of the AMA's Competition in Health Insurance: A Comprehensive Study of U.S. Markets, which looked at market concentration in 2016, has found that in 43 percent of metropolitan areas (169 out of 389), a single health insurer had captured at least a 50 percent market share—an 8 percent increase in such concentrations in a little over two years.

According to the report, the study is “intended to help researchers, policymakers and regulators identify markets in which consolidation among health insurers may cause anti-competitive harm to patients and the physicians who care for them.” There’s less competition among commercial health insurers in high market concentrations, which then exposes those markets to insurers flexing their muscles by boosting premiums above competitive levels.