Once you (and your partner) have considered all of these logistical and financial factors and you have a real pregnancy that will mandate a real maternity leave, next you need to figure out with whom you will be negotiating your leave.  Likely candidates include medical school advisors or deans, residency or fellowship directors, medical directors, division director, and department chairs.  If it is not immediately obvious to you who will be the final decision maker, you can ask for advice from other medical students or physicians in your organization who have taken a maternity leave, if they exist.  In academic medicine, it is ultimately your chair that has the final say even if she/he is not your immediate supervisor.