Leg cramping could be a result of low potassium or low calcium. Leg cramps are very common and happen more in the last trimester as the kidneys are working really hard to pump all that extra blood that pregnant women have. So your kidneys may be filtering out more of the calcium and potassium that we normally have.
The best thing a woman can do is to have more calcium in the form of dairy or Tums, and eat more potatoes, broccoli, and bananas (which have more potassium and more calcium).