I have posted this theory before.
I think some "troll" threads are people who are posting about something that happened to them in the past, that they never got closure or support for.
When my ex-h left me I thought he was having an affair but he denied it vehemently. After reading MN I think I was right. If I was still hung up on him (I'm not!) I could imagine describing the whole break up, he said, I said etc, as if it was actually happening now, but really just to get my own opinions validated. I must stress that I never have done this!
When I posted this theory on another thread, someone pm'd me to say she had done what I had said, to make sense of things and so had a friend of hers.
I see this in a number of types of thread. From time to time someone will say they think they might have been raped but are not sure. They get lots of advice to not shower and call the police immediately but don't take it to the other posters' immense frustration. I think this is because they can't take the advice, as the incident happened years ago.
I think the premature twin "troll" might be someone who lost premature twins a long, long time ago. Nowadays they might have survived but back then there was no chance, and she didn't get much support or sympathy, and she is reliving it in an attempt at coming to terms with it. 