Aetna, one of the nation’s largest insurers, announced last Friday that it was pulling out of Maryland’s health insurance exchange after regulators demanded that it slash premiums the company had proposed by 29 percent, the Baltimore Sun reported.

The company, which recently purchased Coventry Health Care, said that it wouldn’t be able to cover its costs if it charged what regulators were demanding.

As I wrote in a column last month, a number of insurers have been opting not to participate in the health insurance exchanges created by President Obama’s health care law and in some cases, they have been exiting state individual insurance markets entirely.

For instance, Aetna – along with UnitedHealth – has already announced it was pulling out of the individual market in California. On July 19, Anthem Blue Cross, California’s largest insurer of small businesses, pulled out of the Obamacare small business exchange.

The design of Obamacare was premised on the idea that the new exchanges would attract many insurers, giving consumers a wide array of choices that would foster the type of competition that would drive down premiums. Instead, trends over the past few months suggest the law, if anything, will increase consolidation in state insurance markets.

And as an early an enthusiastic adopter of Obamacare, Maryland is a state that the law’s supporters are holding up as a model.