He is a clinician, researcher and medical educator best known for his work in the development of egg and embryo donation, fertility care of HIV-seropositive patients, and reproductive bioethics.

He currently is Professor and Chairman of Obstetrics, Gynecology and Reproductive Sciences at Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey.

Sauer was the Chief of the Division of Reproductive Endocrinology at Columbia University Medical Center in New York City for twenty-one years, where he was also the program and laboratory director of the Center for Women's Reproductive Care,[1] and a tenured professor and vice-chairman in the Department of Obstetrics and Gynecology at the College of Physicians and Surgeons, Columbia University.

Sauer achieved the world's first donor egg pregnancies in older menopausal women while serving as an associate professor at the University of Southern California in Los Angeles.

Sauer's other projects included the introduction of methotrexate for the nonsurgical treatment of ectopic pregnancies, and more recently the use of semen washing techniques to prevent the transmission of HIV in couples wishing to conceive when the wife is uninfected.