Pregnant 4 months belly hard what to return a responsibility

4 months of pregnancy when showing a feeling of hard belly, is because of uterine smooth muscle contraction caused by a symptom. There is no obvious abdominal pain symptoms, it belongs to ineffective uterine contractions, intrauterine pressure does not change significantly, will not show fetal descent, cervical dilation phenomenon, can be gradually relieved after rest. Normal is because of mental stress or walking too long, sexual stimulation and induced. Contractions with obvious abdominal pain are effective contractions. Increased intrauterine pressure may cause fetal descent, cervical dilation, and continued presence may cause threatened abortion. The normal cause is the persistence of adverse stimuli, or cervical insufficiency, or abnormal development of the fetus itself.