Leg cramps — painful involuntary muscle contractions that typically affect the calf, foot or both — are common during pregnancy, often striking at night during the second and third trimesters.

While the exact cause of leg cramps during pregnancy isn't clear, you can take steps to prevent them. For example:

• Stretch your calf muscles. Although evidence is lacking, stretching before bed might help prevent leg cramps during pregnancy. Stand at arm's length from a wall, place your hands on the wall in front of you and move your right foot behind your left foot. Slowly bend your left leg forward, keeping your right knee straight and your right heel on the floor. Hold the stretch for about 30 seconds, being careful to keep your back straight and your hips forward. Don't rotate your feet inward or outward. Switch legs and repeat.
• Stay active. Regular physical activity might help prevent leg cramps during pregnancy. Before you begin an exercise program, make sure you have your health care provider's OK.
• Take a magnesium supplement. Limited research suggests that taking a magnesium supplement might help prevent leg cramps during pregnancy. Make sure you have your health care provider's OK to take a supplement. You might also consider eating more magnesium-rich foods, such as whole grains, beans, dried fruits, nuts and seeds.
• Stay hydrated. Keeping your muscles hydrated might help prevent cramps. Your urine should be relatively clear or light yellow in color if you are properly hydrated. If your urine is darker yellow, it might mean that you're not getting enough water.
• Get adequate calcium. Some research suggests reduced levels of calcium in your blood during pregnancy may contribute to leg cramps. All women, including pregnant women, should get 1,000 milligrams of calcium a day.
• Choose proper footwear. Choose shoes with comfort, support and utility in mind. It might help to wear shoes with a firm heel counter — the part of the shoe that surrounds the heel and helps lock the foot into the shoe.

If a leg cramp strikes, stretch the calf muscle on the affected side. Walking and then elevating your legs might help keep the leg cramp from returning. A hot shower, warm bath, ice massage or muscle massage also might help.