The reason people think that this (and other things like that) work is because, frankly, there's a 50/50 chance that whatever they say is going to be what you have. Usually, the people who do it and it's wrong just figure, whatever, that was stupid, and forget about it. But, if they happen to have guessed right, then people get all freaked out because they were right.
It's like saying hey, if I flip a coin with my right hand, I'm going to get heads, but if I flip it with my left hand, I'm going to get tails. Well, of course, some of the time, that will be true, but that doesn't make it an accurate statement or mean that knowing what hand I use to flip the coin (or, in this case, what way a ring moves) is going to be reliable.
If you want to know what you're having, do an ultrasound, or, better yet, do an amniotic fluid test...
at 7:34 AM on Dec. 11, 2009