It'd also be worth pointing out that the STEM "gap" isn't just in people choosing fields, it's also the fact that females score lower on all kinds of science tests and assessments. This bias shouldn't exist, regardless of what job people ultimately choose, unless you want to engage in some hoary stereotyping that "explains" why women don't have the "spatial acuity" for physics or blah blah.
Among mere practicing physicians, a group where men and women are basically at parity, women make 80% what their male counterparts do, and only 20% of medical school faculty are women.
There is the more fundamental metaphysical question -- even if we define STEM fields to include medicine and we can get the diversity to 50-50, why should we have to? Why would their be so many more male physicists than female ones (again without engaging in insulting stereotypes and gender essentialism)?