I didn't know that. I went and googled cramping in pregnancy to see if I can trace down the source of the info I gave above and it seems to be quite common advice given on pregnancy websites to try stretching your calf muscle by pulling your toes toward you. Otherwise they say that you can try applying a hot or cold pack to the affected site. Stretching worked for me, but maybe talk to your doctor about it if there is the potential for it to be dangerous.