A blood clot in a pregnant woman indicates abnormal bleeding in the uterine cavity. The clinical symptoms that accompany this symptom vary depending on the week of pregnancy in which it occurs, and the possible causes are completely different. In early pregnancy, if a blood clot comes out of the vagina, if the pregnancy has been diagnosed as intrauterine, it is mostly considered to be a symptom of miscarriage. It is possible that the embryo has stopped developing, or it may simply be a pre-eclampsia, and an ultrasound examination is needed to further clarify the diagnosis. If no ultrasound examination has been performed and it is uncertain whether the pregnancy is intrauterine or ectopic, the symptoms need to be considered whether the pregnancy is a ruptured ectopic miscarriage, and ultrasound examination is also needed to make a clear diagnosis. If it occurs in the middle or late stage of pregnancy with abnormal vaginal bleeding but is not accompanied by abdominal pain symptoms, it is considered to be caused by a low placental position.