There are several reasons for the hardness below the belly button in the 4th month of pregnancy: first, it may be a condition caused by hormonal secretion in the body during pregnancy, which stimulates the abdomen, and if the degree of hardness is mild, there is basically no need for treatment. Secondly, it may also be due to pseudo contractions during pregnancy, some women’s bodies are stimulated, which can lead to irregular contractions, this situation is more likely to trigger a pre-eclampsia, so you must take proper rest, it is best not to stimulate the body often, and it is best not to do too much physical work. Third, it may also be caused by dietary factors, if often eat stimulating food, will also lead to this situation, so usually must pay attention to a light diet, it is best not to overeat, so as not to affect the growth and development of the fetus.