Leg cramps affect almost half of all pregnant women.1 The cause of leg cramps during pregnancy is not fully known, but they may be caused by reduced levels of calcium in the blood or increased levels of phosphorus. Leg cramps are more common in the second and third trimesters of pregnancy and happen most often at night.
There is no evidence proving that increasing your intake of calcium or potassium will prevent leg cramps.1
If you get a leg cramp:
Although uncommon, a blood clot can form in a deep vein of the leg (deep vein thrombosis, or DVT) during pregnancy. DVT can be life-threatening and requires medical treatment.
Symptoms of DVT include severe leg pain or tenderness (not cramps), swelling of the leg and foot, and fever. The leg may have a bluish (cyanotic) or pale color and may be either hot or cold to the touch. If any leg pain persists (especially with leg swelling), contact your health professional immediately.
Citations
WebMD Medical Reference from Healthwise