The blood in preterm miscarriage comes mainly from the capillaries in the uterus and the gestational sac. One of the main effects of progesterone is to inhibit the contraction of the smooth muscle of the uterus. When progesterone decreases in preterm miscarriage, the uterus will contract and the uterine wall and the gestational sac will begin to peel away from each other, resulting in the rupture of local capillaries and the flow of blood, which manifests as vaginal bleeding. The vaginal bleeding in pre-eclampsia is usually small, and due to the oxidative reaction that may occur in the vagina, the blood seen by the pregnant woman is mostly brown or dark red, and may be accompanied by bloody leucorrhea, paroxysmal lower abdominal pain or lower back pain. When a pregnant woman has a pre-eclampsia, if the symptoms are mild, there is a chance of fetal preservation treatment. The pregnant woman can follow the doctor’s prescription to use hormones and actively keep the fetus. As the treatment progresses, vaginal bleeding stops and the symptoms gradually disappear, the pregnancy can continue. When vaginal bleeding continues to increase, abdominal pain continues to worsen, and there may be a feeling of cramping in the small abdomen at the same time, it indicates that the condition has developed into unavoidable miscarriage. At this time, the opening of the cervix is visible through gynecological examination, and birth preservation is ineffective, and the pregnant woman must undergo abortion or surgical induction of labor to remove the dislodged pregnancy sac, otherwise serious intrauterine infection, uterine bleeding and even life-threatening may occur.