From Andrew Sullivan: the strange and involved narrative of the birth of Trig Palin. (while Sullivan's synopsis is well done, I echo his advice and urge you to read the contemporary Anchorage Daily News reports here and here, and the long after-the-fact NYT report here, even or especially if you are not interested in Sullivan's commentary and interpretation.)
I will keep myself from posting my own entirely-non-fact-based theorizing, since I, as a fiction writer, am prone to the occasional fancy. However, what strikes me about this particular story is that, maddeningly, Palin's actions make more sense and not less when explained by increasingly wild speculations. The continual reasonable questions of "why, why, why?" find a single response. It's a mystery.