For a few years, most publicly traded U.S. health insurers seemed to follow a common pattern: They increased their net income quarter after quarter.

This quarter, the idea that a health insurer is as steady as a utility company or a railroad used to be years ago seems to have sputtered out.

UnitedHealth Group Inc., Minnetonka, Minn. (NYSE:UNH), reported higher net income for the second quarter than it did for the quarter of 2011, but WellPoint Inc., Indianapolis (NYSE:WLP), reported a drop, and now Coventry Health Care Inc., Bethesda, Md. (NYSE:CVH), a midsize insurer, and Molina Healthcare Inc., Long Beach, Calif. (NYSE:MOL), a public plan specialist; have also reported year-over-year decreases in earnings.

Other companies posting weaker net income include Magellan Health Services Inc., Avon, Conn. (Nasdaq:MGLN), a company that manages behavioral health services and other specialty health services, and eHealth Inc., Mountain View, Calif. (NYSE:EHTH), the company that runs the eHealthInsurance.com website.

Coventry is reporting $92 million in net income for the second quarter on $3.5 billion in revenue, compared with $224 million in net income on $3 billion in revenue for the second quarter of 2010.

The company ended the quarter providing or administering health coverage for 5.3 million people, up from 4.6 million people a year earlier, and enrollment in the Medicaid plans it insures has reached about 698,000, more than twice what it was a year ago.

The company notes that it is dealing with the new federal Patient Protection and Affordable Care Act (PPACA) minimum medical loss ratio (MLR) rules, which affect the percentage of commercial plan revenue that must be spent on health care and quality improvement efforts. Coventry has been passing broker commissions directly to brokers, to get them out of the MLR calculations, the company says.

Molina is reporting a $37 million net loss for the latest quarter on $1.5 billion in revenue, compared with $17 million in net income on $1.2 billion in revenue for the second quarter of 2011.

Total health plan enrollment increased to 1.9 million, from 1.6 million a year earlier.

Molina executives say the company’s financial performance reflects the challenges involved with the termination of a plan in Missouri and contracts covering aged, blind and disabled people in some service areas in Texas.

Magellan is reporting $27 million in net income for the latest quarter on $806 million in revenue, compared with $34 million in net income on $698 million in revenue for the second quarter of 2011.

EHealth — a Web-based insurance broker — is reporting $2.3 million in net income for the latest quarter on $36 million in revenue, compared with $2.7 million in net income on $36 million revenue in the second quarter of 2011.

The volume of individual and family submitted applications increased 2%, to 103,400 applications.