As someone who has spent time on both sides of PSs, in my opinion applicants tend to have a very, very over-inflated view of how big a part the PS plays. That is understandable as, if I may continue psychologizing, at the time one completes the application, the PS is really the only part of it that one has any control over.
When I have had occasion to evaluate applications, pretty much all the applications that made it to the PS-reading stage were good. Any one of those candidates would have (probably) made a fine resident. Thus, at that point I was looking more for things to provide some shred of justification for eliminating a candidate rather than to include a candidate. If someone's essay looked very unfocused, or if the person did not seem to be able to consistently construct coherent and (mostly) grammatical sentences, or – the kiss of death – if the essay had glaring errors of spelling and basic word usage, that application went near the bottom of the pile. On the flip side, only very occasionally did a PS contain some interesting bit of info that would boost it near the top. Having said that, brevity was always appreciated.
The PS should really be considered an opportunity to: (1) display that you can adequately communicate in written English; (2) express why you are interested in pathology, and perhaps how you see yourself practicing in the future (private vs. academic, etc); and (3) address any "odd" things that may appear elsewhere in your application.
(1) and (2) you should ALWAYS do, fully and clearly. As for (3), you should be a little strategic. You don't want to draw excessive attention to something that might be looked upon dubiously. Remember, they are looking for reasons to eliminate you.
Given your situation, as explained above, I would imbed in your essay one paragraph that explains, simply and clearly, why you did what you did. Put a positive spin on it. DO NOT use the phrase "took a year off." Confidently say, as you do above, you discovered pathology late in medical school and wanted to do path rotations to be sure you were making the right decision. The following year you worked in a pathology research lab, and, your "biggest accomplishment," had a baby. (Be sure to include "biggest accomplishment." Corny? Yes. But people love that stuff - and best of all, it's true.) DO NOT apologize. DO NOT dwell on what a "difficult decision" it was. DO NOT use the word or invoke the concept of "multifactorial."
Far more evaluators will be impressed with your having known what was best for you, and doing it, than be put off by your "taking a year off" (which, remember, you didn't). In your final application, include an LOR from someone with whom you worked during that year.
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