The abdomen is like menstrual cramps in the fourth month of pregnancy, which can be considered to be caused by physiological contractions, pre-eclampsia, ectopic pregnancy, gynecological and other diseases. 1. physiological contractions: simply manifested as a slight abdominal pain sensation, without other discomfort symptoms, mainly due to the increase in the size of the uterus, which will compress the surrounding tissues and pull the ligaments, resulting in changes in the tension of the muscle groups, resulting in a change in the muscle groups. Abdominal pain occurs. It is a physiological phenomenon, no special treatment, usually pay attention to more rest can be; 2, pre-eclampsia abortion: 4 months of pregnancy abdomen like menstrual cramps, pain is light, may also be accompanied by vaginal bleeding, in the exclusion of ectopic pregnancy, more considered pre-eclampsia abortion. Pregnant women need to go to the hospital accompanied by their family members for corresponding examination in time, and if necessary, carry out fetal preservation treatment, such as the application of progesterone, while pregnant women pay attention to bed rest and avoid strenuous activities, and also need regular maternity checks at a later stage to observe the growth and development of the fetus in the uterine cavity; 3. Ectopic pregnancy: 4 months of pregnancy, the abdomen is like menstrual cramps, the pain is severe and may be accompanied by vaginal bleeding, consider ectopic pregnancy, such as uterine horn pregnancy, intermyometrial pregnancy, you need to go to a regular hospital immediately and under the guidance of a professional doctor for timely surgical treatment to avoid hemorrhage and affect your health; 4. gynecological and other diseases: gynecological diseases such as pelvic inflammatory disease, in addition to abdominal pain, are accompanied by symptoms such as mucous-purulent discharge and itching from the cervix and vagina. Other diseases, such as appendicitis and gastroenteritis, can cause abdominal pain of different degrees and require timely medical treatment under the guidance of a doctor.