I got leg cramps when I was pregnant too. For me it was not enough calcium. The first place that your body takes it from is your muscles, hence the leg cramps. A few weeks later I started getting heartburn, so I needed to take Tums throughout the rest of my pregnancy. The Tums gave me the calcium that I needed and my leg cramps went away.
Maybe this will work for you, or maybe it's something else. Good luck!