Bleeding in the third month of pregnancy is naturally not a good thing, it is an abnormal phenomenon, you need to seek medical attention in time, conduct relevant examinations, and if necessary, carry out surgical treatment for birth control or abortion, several common causes of bleeding are as follows: 1, pre-eclampsia abortion: vaginal bleeding is a common clinical manifestation, the fetus is not able to stabilize the bed, with the shedding of the vaginal uterine lining, vaginal bleeding can occur; 2, ectopic pregnancy. With the increase of fetus, the local environment is not enough to survive, resulting in vaginal bleeding due to rupture of local blood vessels, which can endanger the life of pregnant women, prone to hemorrhage and cause hemorrhagic shock; 3. Embryonic arrest: after embryonic arrest, due to the absence of hormone release, it will lead to the loss of hormonal support of the meconium and shedding, manifesting as a small amount of vaginal bleeding; 4. Placental hypoplasia: the lower part of the uterus is constantly stretched, while the placental tissue attached to the lower part of the uterus The placenta tissue cannot be stretched accordingly, and the blood vessels at the placenta attachment will rupture and vaginal bleeding will occur; 5. Cervical lesions: if cervical inflammation, cervical polyps, cervical precancerous lesions, etc. occur during pregnancy, vaginal bleeding may occur. If pregnant women have symptoms of vaginal bleeding, they need to go to hospital immediately for examination to clarify the cause of bleeding and treat the symptoms under the guidance of doctors.