If the buttocks cramp during pregnancy, it may be caused by the following reasons: 1. It may be caused by the rapid growth of the fetus or the rapid increase of water. At this time, the load on the front of the body will increase rapidly in a short period of time, in order to maintain balance when the body is upright, the muscles of the back, such as the low back and buttocks will need to maintain tension for a long period of time, and it is possible to produce muscle spasms in the buttocks. 2, there may be insufficient exercise. There are many patients who do not exercise regularly before pregnancy, resulting in very poor muscle strength in the lower back and buttocks. During pregnancy, these parts of the muscles need to be used frequently to generate force, once this situation occurs, may produce muscle spasm due to insufficient muscle strength. 3, may be complicated by peripheral nerve related lesions, for example, during pregnancy, due to the wide range of physiological curvature, rapid changes, may be triggered by lumbar disc herniation or sciatica and other diseases. Once this kind of disease occurs, it will produce radioactive pain in the buttocks and lower limbs, and may cause muscle spasm in the buttocks.