Hope this helps:
What is causing my painful leg cramps?
Your heart, kidneys, and circulatory system work extra hard to help you function normally during pregnancy, and your muscles, which are bearing the increasing weight of your pregnancy, feel the strain, too. So as a result, your tired leg muscles may seize up and cramp in protest, especially during your second and third trimester. The pain can wake you from a deep sleep.
Muscle fatigue isn't the only reason you may be suffering from leg cramps. Too much phosphorus (found in processed meat, snack foods, and soda) and too little calcium and potassium circulating in your blood can also cause muscle spasms.
And a third reason is that as your uterus expands, it can put pressure on the nerves leading from your trunk to your legs.
Is there anything I can do to stop it from happening?
Try our BabyCentre tip and eat a banana or drink a glass of milk before bed for a quick calcium and potassium boost. Don't take any herbal or vitamin supplements without first discussing it with a medical herbalist.
Here are some other tips for keeping muscle spasms at bay:
Avoid standing or sitting with your legs crossed for long periods of time.
Rotate your ankles and wiggle your toes when you sit, eat dinner, or watch TV.
Stretch your calf muscles (see How to get rid of leg cramps, below) several times before you go to bed.
How to get rid of leg cramps
If you do get a cramp, stretch the muscle straight away. Straighten your leg, heel first, and gently flex your ankles and toes. It might hurt at first, but the pain will gradually go away. You can also relax the cramp by massaging the muscle or warming it with a hot-water bottle. Walking around for a few minutes may help, too.
If your muscle pain is constant and not just an occasional cramp, or if you notice swelling or tenderness in your leg, contact your doctor. In rare cases (one in 2,000) a pregnant woman can develop venous thrombosis, or a blood clot, which requires immediate medical attention