The vague pain in the right side of the abdomen in the third month of pregnancy is mostly considered to be physiological abdominal pain caused by the enlargement of the uterus, while the presence of pathological causes is not excluded. I. Physiological causes: 1. Uterus enlargement: when pregnant women are in the third month of pregnancy, the uterus begins to gradually increase in size, which will involve pain in the muscles and ligaments. This is a normal physiological phenomenon during pregnancy, and generally does not require treatment. At this time, pregnant women should pay attention not to strain, more bed rest, the pain can basically be relieved; 2, the right rotation of the uterus: after pregnancy, most pregnant women will appear right rotation of the uterus, so the more sensitive pregnant women will feel the right side of the abdomen vague pain. This is a relatively normal phenomenon, no special treatment is needed, generally continue to observe can. Second, pathological reasons: 1, pre-eclampsia miscarriage: early pregnancy, fetal pre-eclampsia miscarriage will also make pregnant women appear abdominal pain, usually accompanied by a small amount of vaginal bleeding, the color is often dark red or bloody leucorrhea. It can be manifested as vague pain in the right side of the abdomen, sometimes lasting for a long time and accompanied by pain in the lower back. It is recommended that pregnant women take proper rest and avoid intercourse. In general, luteal insufficiency can be treated by progesterone injection or oral progesterone preparations, while pregnant women with hypothyroidism can take oral thyroid tablets as prescribed by the doctor. After the vaginal bleeding stops, if the ultrasound examination indicates that the fetus can survive, the pregnancy can be continued; if the examination indicates that the fetus is stunted, the pregnancy can be terminated under the guidance of the doctor; 2. ectopic pregnancy: most pregnant women have abdominal pain on one side when ectopic pregnancy occurs, and if the gestational sac is in the right fallopian tube, it may lead to pain in the right side of the abdomen, and there may also be irregular vaginal bleeding. Clinically, the treatment of ectopic pregnancy is mainly surgical and pharmacological, which can be chosen from conservative surgery or radical surgery according to the physical condition of the pregnant woman and whether she has fertility requirements. Conservative surgery is mainly suitable for pregnant women who have fertility requirements and the opposite fallopian tube has been removed or diseased, while radical surgery is mainly suitable for pregnant women who do not have fertility requirements or who are in shock. If the above reasons are excluded and the pain still cannot be relieved, it should be clarified whether there are diseases of the digestive system (appendicitis, gastroenteritis), urinary system (kidney stones, ureteral stones), gynecological comorbidities (ovarian tumors) and other diseases.