The research (and our experiences) seem to agree most times about this - magnesium helps those who didn't have enough magnesium to begin with. It doesn't help the rest of us much at all. Same with many other vitamins and minerals. The form of magnesium doesn't seem to matter. If you think you might be deficient, do try it. If you are deficient, it may help.
Iron is different. You can seem to have normal iron levels - both of serum ferritin and hemoglogin - and taking it can help a lot. It can also be constipating - not fun when pregnant! And, the form does seem to matter more. Here's a link to a WED Foundation publication about iron:
http://www.rls.org/Document.Doc?id=2078 .
They also have a Pregnancy and RLS/WED publication.
https://www.rls.org/document.doc?id=2206 There are many others - but many are available only to members. If you join, you can see them all.
Regular exercise may help. Not heavy, hard or lengthy. Just walking or other mildly aerobic exercise 30 minutes or so 5 days a week. Studies have shown this level to be the best.
This is such a weird disorder - sugar, artificial sweeteners, caffeine - they all can trigger some people. Stopping doesn't help everyone, but it's worth trying.
This post may be helpful to you - there are many things we can try that help some of us (pregnant or not) and it turns out they are all related to ways to naturally increase dopamine. Lack of dopamine at critical times during the day/night is related to WED.
viewtopic.php?f=20&t=8906Of course, massage often helps. But, finding someone to do it isn't always an option. Compression stockings help many, but I don't know if they are safe during pregnancy. You'd have to ask your doctor.
a few other things can impact WED during pregnancy, such as gestational diabetes. If you have any other health conditions, they can cause issues. Getting them under control often will help.