Insurer-owned clinics are taking on hospitals and physicians for patients

For example: UnitedHealth Group's Optum arm has amassed doctor practices, surgery centers and urgent-care clinics. Aetna — which was acquired by CVS — has MinuteClinics. And Blue Cross & Blue Shield of Texas has recently opened clinics with a partner company.

• Some plans favor care received by their own providers, although how many doctors a plan owns in any given market varies greatly.
• "It's very worrisome for hospitals," Chas Roades, a health-care consultant, told WSJ. "Suddenly, the plan you're relying on for payment is also competing with you at the front end of the delivery system."

The big picture: Plans built around their own clinics generally have more limited doctor and hospital options, but that can lower premiums.

• It can also benefit insurers by keeping revenue all under the same umbrella.

Go deeper: Insurers may not pay for care they've approved