A common cause of leg cramps at night in the fourth month of pregnancy is calcium deficiency. During the fourth month of pregnancy, the fetus in the body grows and develops faster and requires more nutrients, especially electrolytes and minerals. If you do not pay attention to calcium supplementation at this time, it is likely to lead to insufficient amount of calcium in the body. When calcium is not enough, it causes low calcium, which leads to spontaneous muscle contractions called cramps. Pregnant women can get relief by supplementing calcium with calcium-rich foods, such as milk, nuts, seafood, such as shellfish, etc., or by getting proper sun exposure, which can promote calcium absorption and increase the calcium content in the body through these integrated ways, so as to prevent cramps.