Some facts from the web.. 4-5 years old, and I suspect the trend is continuing...
Using data from a variety of sources, the Association of American Medical Colleges (AAMC) 2015 Report on Residents identified the top specialties among 86,439 residents in the graduate medical education class of 2013-2014.
Based on key findings, women make up a larger percentage of residents in:
Family medicine (about 58 percent)
Psychiatry (about 57 percent)
Pediatrics (about 75 percent)
Obstetrics/gynecology (about 85 percent)
The data show male residents prefer to specialize in:
Surgery (about 59 percent)
Emergency medicine (about 62 percent)
Anesthesiology (about 63 percent)
Radiology (about 73 percent)
Internal medicine (about 54 percent)
Another odd thing I discovered the most sex lopsided state for doctors is Idaho. 671 female MD's vs 2192 males.