More than three months pregnant stomach hardness, may be the uterus contraction, may also be holding urine, constipation, diarrhea, miscarriage, etc., if necessary, need to consult a doctor to find out the cause. 1. contractions: some pregnant women due to the core muscle group strength is not enough or low body weight, subcutaneous fat is too thin, the uterus is easy to increase the influence of the external environment, so some contractions of the feelings, self-conscious stomach hardening. 2. Holding back urine, constipation or diarrhea: Because the front of the uterus is the bladder, the back is the intestinal tube, if the morning holding back urine leads to the enlargement of the bladder, long-term constipation or diarrhea affects the peristalsis of the intestinal tubes, etc., may stimulate the uterus, so that in the third trimester of pregnancy, you feel the stomach hardened state. 3. Pre-eclampsia: However, if there is abdominal pain, vaginal bleeding and other symptoms at the same time as the hardening of the stomach, then there may also be the phenomenon of pre-eclampsia, which should be promptly consulted by the doctor to give targeted treatment. During pregnancy, you should follow the doctor’s instructions to have a regular checkup, and if you feel unwell, it is recommended that you go to the hospital for a checkup in a timely manner, so as to clarify the cause of the illness and follow the doctor’s instructions.