Though the ultimate fate of President Obama's health care reform law is unclear, a new survey estimates it has already benefited 6.6 million young adults that were able to obtain insurance coverage under their parents' health plans.

The Commonwealth Fund, a private health care reform advocacy group, surveyed more than 1,800 young adults between ages 19 to 29 and estimated that about 13.7 million young adults across the U.S. joined or stayed on their parents' plans in 2011. Of those, 6.6 million would not have been able to stay on their parents' plans before the passage of the Patient Protection and Affordable Care Act, the group says.

Previously, young adults could lose their coverage under their parents' health plans once they left high school if they did not go to college, or once they graduated from college, or if their employer offered health insurance.

But PPACA, signed into law in March 2010, provided a wider safety net for young adults by requiring insurance plans with dependent coverage to cover adult children until they turn 26.

The effect has been dra­matic: Between September 2010 and June 2011 the number of insured young adults increased by 2.5 mil­lion, likely as a result of this new provision, the report says.

But there are still gaps in health insurance coverage, as not every young adult has parents with health insurance. The survey found that nearly two in five young adults between 19 and 29 years old were uninsured at some point in 2011.

The uninsured burden primarily falls on young adults with low or moderate incomes. Nearly three-quarters of those who didn't have health insurance when they were surveyed had incomes under two and a half times the 2011 federal poverty level ($10,890 for a single person), the survey found.

Medical cost burdens also weigh heavily on young adults, the report found: 36% of those surveyed had problems with medical bills or were paying off medical debt. Among that group, 43% reported using all of their savings to pay for medical expenses, 32% said their medical costs made them unable to make student loan or tuition payments, and 31% said they'd delayed plans for school or work. Another 28% said they were unable to pay for basic necessities like rent, food or heating because of their medical bills.

While the Affordable Care Act has already provided a new source of coverage for millions of young adults at risk of being uninsured, more help is needed for those left behind, Commonwealth Fund Vice President Sara Collins, lead author of the report, said in a statement on Friday.

PPACA includes other provisions scheduled to go into effect in 2014 aimed at closing the uninsured gap, including expanding Medicaid eligibility to all individuals with income up to 133 percent of the federal poverty level, not just adults with children.

In 2014, the law also requires U.S. states to establish standardized health insurance exchanges, and insurers will not be able to discriminate against or charge higher rates to people with pre-existing medical conditions.

But whether or not PPACA will still be alive by 2014 isn't certain -- the US Supreme Court is currently weighing whether or not the health care law's mandate requiring individuals to buy health insurance is unconstitutional. And if the purchase mandate is stricken, it's unclear how much of health reform can be salvaged from the remains.