In Houston, expectant mothers receive prenatal care at Harris County Hospital facilities—regardless of whether they have documents proving they're American citizens.

The thinking is that the care prevents other health problems down the road. But it comes at a cost. Between limited preventative and emergency care, illegal immigrants account for 12 to 14 percent of Harris County Hospital District's $1.1 billion annual budget, says King Hillier, vice president of public policy and government relations.

"We're not going out there doing elective surgeries or face-lifts," Hillier says. "We're providing the bare level of care for these folks."

That care is paid largely by local taxpayers. The federal government, which is in charge of policing America's borders, kicks in very little to care for covering undocumented immigrants. In 2005, the feds contributed just over $100 million for all of Texas.

Illegal immigrants cost the U.S. health system $4.3 billion a year when all levels of government are accounted for, according to a report by Steven A. Camarota, director for research at the Center for Immigration Studies. The majority of costs are ultimately paid by local residents, although emergency care for illegal aliens is funded by Medicaid. Local citizens pay when public hospitals, like Harris County Hospital District, provide free care. But locals also pay because charity care drives costs for fully insured people.

"It gets passed on like a hidden health care tax," says Jim Haynes, chief financial officer of the Arizona Hospital and Healthcare Association. "Hospitals negotiate with insurance plans, and one of the elements that goes in there is the care that goes for that population. It does get passed on."

So President Obama and other Democrats may pledge that tax dollars won't go toward caring for undocumented immigrants, but they're really just shifting the cost for someone else to pay. Hospital officials in states like Texas, Arizona, and California say it's not fair. There's been limited federal money to fix what hospitals say is a federal issue. Illegal immigrants number almost 12 million, or 4 percent of the U.S. population. That number is up more than 40 percent, from 8.4 million in 2000, according to the Pew Hispanic Center.

"They say we won't cover illegals, but America's health providers are stuck with the cost," says Kevin Burns, chief financial officer at University Medical Center in Tucson.

“While there is funding under current law to help offset uncompensated care, the best way to tackle this problem is through comprehensive immigration reform, which is another priority for this administration,” the White House says in a statement.