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.

What are cramps and why are they common during pregnancy?

Cramps are a sudden, sharp pain, usually in your calf muscles or feet. A cramp is a sign that your muscles are contracting very tightly when they shouldn’t be. They usually happen at night and are more common late in your pregnancy. They can be very uncomfortable, and it can be hard to know what to do.

There are many suggested reasons for cramps while you’re pregnant – carrying extra weight, changes to your metabolism, having a vitamin deficiency, being too active or not being active enough. The truth is that nobody really knows.

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.

When can I expect leg cramps to end while I'm pregnant?

Really bad cramps (like a charley horse) can cause pain for a few days, and that's nothing to worry about.

Leg cramps are especially common in the second half of pregnancy, when pregnancy weight gain, increased swelling and overall fatigue are at their high points — and interruptions to your sleep are most frustrating.

Unfortunately for most women, leg cramps last through the third trimester of pregnancy. Taking steps to reduce leg cramps (drinking lots of water, eating a well-balanced diet, stretching) can help keep them at bay.

When to see your doctor about leg cramps

If the pain is severe and persistent (and if you notice swelling, warmth or redness in the area), talk to your practitioner. In very rare cases you could have a blood clot in a vein known as deep vein thrombosis (DVT) that requires medical attention.