Even after the Affordable Care Act was passed, many unknowns remained, says Chris Renz, a partner and Northern California leader of global consulting firm Mercer's health and benefits business.

"Regulations had not been issued for many of the health care provisions," he says.

The list of women's preventive services that health plans must fully cover wasn't hammered out until August of 2011, for instance. "Employers who lost grandfathered status early on have no choice but to implement that standard," Renz says.

Still, he says, "Our surveys have been fairly consistent -- the number of grandfathered plans will continue to dwindle each year."

So are you at a disadvantage if you're in a grandfathered plan?

"I don't think it's clear-cut from an employee's perspective," Stone says.

A grandfathered plan might provide you with more affordable health insurance overall. Remember, your employer can't significantly increase your costs, including the portion of premium you pay to keep a plan grandfathered. So even if it doesn't fully cover preventive care, a grandfathered plan might cost you less than a non-grandfathered plan when you add and compare the premiums, deductibles, and other out-of-pocket costs.

An overview of grandfathered health plans can be found at HealthCare.gov.

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