"As Americans have begun shopping for health plans on the insurance exchanges, they are discovering that insurers are restricting their choice of doctors and hospitals in order to keep costs low, and that many of the plans exclude top-rated hospitals.... The result, some argue, is a two-tiered system of health care: Many of the people who buy health plans on the exchanges have fewer hospitals and doctors to choose from than those with coverage through their employers. A number of the nation's top hospitals -- including the Mayo Clinic in Minnesota, Cedars-Sinai in Los Angeles, and children's hospitals in Seattle, Houston and St. Louis -- are cut out of most plans sold on the exchange."