— People who have Anthem Blue Cross and Blue Shield in Connecticut as their health insurer will face more expensive, out-of-network rates at Middlesex Hospital starting Jan. 1.

Anthem, the state's largest health insurer in terms of membership, and Middlesex Hospital have negotiated terms of a contract for months, but the two sides were unable to agree on a deal, according to Wallingford-based Anthem.

The previous contract ended Monday. This is the most recent in a continuing series of contract battles between health insurers and hospitals. In general, insurers argue that they are trying to hold down medical costs for customers while hospitals say they are only asking the price to provide quality treatment for patients.

"We value this hospital and their role in our network; however, the level of increase they are demanding is unreasonable to pass along to our customers," said Anthem spokeswoman Sarah Yeager.

Anthem told its members earlier in December that Middlesex Hospital could be eliminated from the insurer's network of medical providers if the two sides didn't agree on a contract by the Dec. 31 deadline. Anthem is referring its members to other hospitals.

Neither the hospital nor the insurer on Monday would say how many patients who have Anthem have used the hospital's services in the past year. The sticking points also aren't clear, though in many contracts, the insurer and hospital disagree about the price the insurer should pay for services, such as surgeries, x-rays, diagnostic tests and other clinical costs.

"We're fortunate that we have other in-network providers and hospitals in the area and throughout Connecticut who can meet our members' health care needs," Yeager said.

Middlesex Hospital declined to comment beyond acknowledging that the contract was set to expire Monday.