The biomedical research workforce plays a crucial role in fostering economic growth and improving public health through discoveries and innovations. This study fills a knowledge gap by providing a comprehensive portrait of this workforce and retention within it. A distinguishing feature is that we use an occupation-based definition which allows us to look 'backward' to field of training and assess the extent to which it has grown more interdisciplinary, and how this differs by gender. The analysis is conducted using restricted-use SESTAT data, the most comprehensive dataset on the scientific workforce in the USA, for the years 1993, 2003, and 2010. Among the findings, we identify differences in interdisciplinarity in training by gender, and these differences have widened. In the retention analysis, which focuses on the 7-year period, 2003-10, we find that retention is negatively and significantly associated with interdisciplinary training for women, but not for men.