ROCKPORT, Maine — The commissioner of the Maine Department of Health and Human Services approved Wednesday the merger of Pen Bay Healthcare and Waldo County Healthcare.

The approval means the two organizations that oversee medical facilities in Knox and Waldo counties will fall under one board of directors. The formation of the singular Pen Bay Healthcare Board is expected to occur Jan. 1.

“Changes in health care financing, regulation and economies of scale have driven them to act more regionally, at least on an ad hoc basis,” a memo from DHHS stated in support of the merger. Commissioner Mary Mayhew signed off on the merger in a Wednesday notice.

DHHS agreed with the Pen Bay and Waldo County organizations that volumes necessary to support high quality specialties are more achievable with a larger patient base. Similarly, the economics of hiring physicians/specialists is more tenable over a larger patient base, in part because changes in physician call coverage expectations require that practice specialties have at least two, sometimes three, four or more physicians to share night and weekend call schedules, the department concluded.

The same is true at administrative levels, the department stated.

Pen Bay Healthcare is the parent corporation of the 99-bed Pen Bay Medical Center in Rockport; the Quarry Hill development in Camden; the Knox Center for Long Term Care in Rockland; Kno-Wal-Lin home health and hospice care, which serves Knox, Waldo and Lincoln counties; the Sussman House hospice center in Rockport; and nearly all physician practices in Knox County.

Waldo County Healthcare is the parent corporation of the 25-bed Waldo County General Hospital in Belfast; Waldo County Home Healthcare Services; Belfast Public Health Nursing Association; Coast Medical Care; Arthur Jewell Community Health Center in Brooks; Donald S. Walker Health Center in LIberty; Lincolnville Regional Health Center; Searsport Health Center; and Stockton Springs Regional Health Center.

The two organizations had total expenses in 2013 of about $210 million, with Pen Bay Medical Center being the largest organization at $106 million.

Pen Bay and Waldo County are subsidiary corporations of MaineHealth, which is the parent organization of numerous hospitals, nursing homes and other health care organizations in southern and central Maine, with the largest being the 606-bed Maine Medical Center in Portland.

The two midcoast area organizations already have the same CEO. Mark Biscone has been head of the Waldo County hospital for more than 31 years. He was appointed Pen Bay’s interim CEO in March 2014.

The two health organizations already have integrated more than 40 programs. The two hospitals are sharing services and positions that include laundry, marketing and communication, nephrology, home health and hospice, urology, vascular surgery, oncology, infectious disease physicians, a chief medical information officer, electronic information, a cardiopulmonary department manager, coverage for the radiology manager’s medical leave, a dentist, grant writing, speech therapy, telepsychiatry service, oncology, an echo sonographer and telestroke services.

Pen Bay became a member of MaineHealth in 2012. Waldo County became part of MaineHealth in 2009.