Dr. O'Brien is Medical Director of Maternal-Fetal Medicine at South Shore Health. 

As a Maternal-Fetal Medicine physician, I am dedicated to caring for women and families navigating high-risk and medically complex pregnancies with expertise, compassion, and individualized attention. 

I strive to integrate evidence-based medicine with a holistic approach that recognizes the physical, emotional, and social factors that shape each patient’s experience. 

I am also committed to advocating for equitable healthcare and improving access and outcomes for marginalized and underserved communities.

I started practicing primary care at Boston Medical Center in 2001 and was part of the Faculty of Boston University's School of Medicine. In 2010, I transitioned to the Quincy and Braintree area to continue serving as a primary care physician and urgent care provider. I graduated from the University of Puerto Rico School of Medicine and completed my residency in Internal Medicine at the Hospital of Saint Raphael/Yale-New Haven Hospital.

William Tollefsen, MD is the EMS and MIH Medical Director for South Shore Health. Dual-boarded in Emergency Medicine and EMS Medicine, Dr. Tollefsen works clinically as an Emergency Physician at South Shore Health in addition to his role as EMS Medical Director.

One of few physicians in the country to receive the prestigious "FAEMS" recognition, Dr. Tollefsen is also the Medical Director for OEMS Region IV, serving 61 cities and towns of the Metro-Boston EMS Council. As the current EMS Medical Director for eight municipal and three private ambulance services on the South Shore, Dr. Tollefsen interacts and provides oversight for over 400 Paramedics.

Dr. Tollefsen graduated from New York Medical College and completed residency training in Emergency Medicine at Harvard University, Brigham and Women's, and Massachusetts General Hospital. He completed a fellowship in Emergency Medical Services and Critical Care Transport at the University of Massachusetts, where he worked as an Emergency Physician and Flight Physician for UMASS LifeFlight. He completed an MBA at the Isenberg School of Management at UMASS Amherst, and holds a Master of Medical Science degree from the Boston University School of Medicine.

A former pre-hospital provider, he is actively involved in EMS system design, paramedic education and Critical Care Transport Systems. He works closely with multiple EMS, Fire and Law Enforcement agencies throughout Massachusetts.

His research interests include systems of care, resuscitation, airway management, and paramedic education.

I grew up in southern Maine and attended Harvard University for my undergraduate education. While at Tufts University School of Medicine and Mount Auburn Hospital in Cambridge, my focus was on primary care medicine. I believe in the dignity of each of my patients. Respect, compassion, and reliability are among my goals in patient care. In my free time, I enjoy the outdoors and the arts, usually in the company of my family. 

My mission is to provide safe, high quality, patient centered care in collaboration with the patient, their family, and other providers on the care team to promote the patient’s goals of care and overall well-being.

It is a privilege to advance my role as a nurse anesthetist at South Shore Hospital. It is of utmost importance to me that I gain the trust of my patients and involve them in the plan of care with effective communication and transparency. Being an advocate for my patients during the perioperative period is my priority. When I am not at work, I enjoy gardening, hiking, spending time at the beach, and cooking.