Yeah it is a little ambiguous on that point. Lost in translation? Just coming back to the forum after my last pregnancy and even in that time more information seems to have come to light. As in all things, no one cause can be blamed, instead there are probably many contributing factors. I read in one article that a distinction had been drawn between two groups; women who had HG up until around the 16 weeks mark and those who had it right through. Makes you wonder if there are two major factors, each of those leading to one or the other (a bit like the types of diabetes). I've been looking for one study that looks at a number of general things like cycle differences, diet (I often think if I wasn't so bad at drinking the right amount of water I wouldn't have gone downhill so quickly last time!), the sort of things you could just find out from surveys. I haven't found one yet but I'm sure it must be out there.
I was on cyclizine last time, it did work, but small price to pay.