whether you need to make up time is often defined by the board you plan to get certified through (assuming that you want to be board certified).
For instance in general surgery (
http://home.absurgery.org/default.jsp?certgsqe) the American Board of Surgery requires that:
"General Requirements
Applicants must:
Within six months after completion of residency, have a full and unrestricted (permanent) license to practice medicine in the U.S. or Canada.
Have satisfactorily completed a minimum of five years of progressive residency education in a program in surgery (general surgery) accredited by the ACGME or the Royal College of Physicians and Surgeons of Canada.
Have obtained, over the five years in the accredited surgery program, at least 54 months of clinical surgical experience, with no fewer than 36 months devoted to the essential content areas of surgery (general surgery) as defined.
Have acted in the capacity of chief resident/senior resident in general surgery for a 12-month period, with the majority of the 12 months served in the final year. The entire chief resident experience must be devoted to the essential content areas of surgery, with no more than four months devoted to any one area.
Have spent no fewer than 48 weeks of full-time surgical experience in each residency year.
Have spent the final two residency years in the same program, unless prior approval for a different arrangement has been granted by the ABS. For residents who will complete their residency training in June 2008 or thereafter, the required 60 months of residency training may be accomplished at no more than three residency programs overall.
Have been the operating surgeon for a minimum of 500 operative procedures in five years and for a minimum of 150 operative procedures in the chief resident year. The ABS does not require a certain minimum number of procedures within a content area."
These items are similar but not identical to the ACGME program requirements(
http://www.acgme.org/acWebsite/downloads/RRC_progReq/440pr703_u704.pdf) which I can't find the minimum weeks required and only says:
"Duration and Scope of Education:
Five years of graduate training in surgery following graduation from a medical school accredited by the Liaison Committee for Medical Education (LCME) is required for the acquisition of the necessary knowledge, technical skill, and judgment. Each resident must be notified in writing of the length of the program prior to admission to the program. All years must be in an accredited program under the guidance of the program director in surgery, regardless of assignments to other disciplines."
I think it is important to remember that while most of us are sympathetic to the need for maternity/paternity leave, the concerns of the board and the RRC are also important to balance, namely that the education of someone finishing a residency can not be given short shrift either. It is essential that you have sufficient exposure and experience in residency to handle things on your own when you are done. Unfortunately, this puts people wishing to take time off to pursue worthwhile things (such as pregnancy), in a bad situation. I have now had a 2 friends that had to extend their residencies for pregnancy related reasons (1 time for pregnacy related complications, 1 time for extended maternity leave). Only you can determine what is best for you and your child. Take what time you need to do what you need to, but realize that there may be consequences and difficult choices ahead.
Well said DaBig, I think we're pretty much on the same page here - as I'm sure most are -but just love to argue extremes 
