Clogged heart arteries and pregnancy are the two most expensive conditions contributing to $790 billion in annual hospital costs in the United States, according to a government study released on Friday. Treatment of atherosclerosis, or hardening of the heart arteries, topped the list at about $44 billion in 2004, the latest year available, the report by the US Agency for Healthcare Research and Quality said. By payer, pregnancies and delivery made up the biggest cost for private insurance and Medicaid, costing hospitals about $41 billion in 2004, the report said. “It is always surprising for people to realize how much hospital care goes to mothers and newborns,” said Roxanne Andrews, author of the report. “Most think of hospitals as places where only the sick go.” The report was based on the largest US database of inpatient hospital charges, kept by the federal government. Health care costs are climbing at more than double the level of inflation, financially straining government coffers and company finances. Medical inflation is exacerbated by the rising number of people without insurance — over 46 million according to the latest figures. They tend seek treatment when they are sickest by going to hospital emergency rooms, the most expensive place to start. Total costs to treat the uninsured were about $36 billion, the report said. Hospital costs in the US are split fairly evenly between the government and private insurance. The federal Medicare program covers about 43 million elderly and disabled, while Medicaid treats about 55 million low-income people. Most of the rest comes from private insurers, typically supplied through employers. Also making the top five most expensive conditions were heart attacks, congestive heart failure and care for newborn infants. Obesity, high cholesterol and blood pressure levels, smoking, and diabetes can all lead to hardening of the arteries. Common surgical treatments include angioplasty, where a catheter is threaded through an artery to the clogged heart artery, and stinting, where a wire mesh tube is used to keep the unclogged arteries clear.