The main reasons why a pregnancy with low progesterone is still bleeding after the injection are that the course of treatment has not yet been reached or that there are chromosomal abnormalities in the embryo or fetus. 1. Have not yet reached the treatment course: one of the important reasons for vaginal bleeding after pregnancy is caused by low progesterone. Before the progesterone reaches the normal value after using progesterone, the symptoms will not be relieved immediately, so even after supplementing the progesterone, the bleeding will still occur. With the prolongation of the treatment time, the bleeding will gradually stop and the symptoms will be relieved, and at the same time, you need to stay in bed after taking the injection and avoid excessive tension and anxiety. 2. Chromosomal abnormality of embryo or fetus: If the disease causes vaginal bleeding after pregnancy, even supplementation of progesterone can not relieve the symptoms, because the main cause of miscarriage in early pregnancy is chromosomal abnormality of embryo or fetus. Therefore, before supplementing progesterone, ultrasound should be done to find out the condition of the embryo or fetus and its appendages, as well as to find out the condition of bleeding in the uterine cavity. If the abortion is incomplete, then there is no need to supplement progesterone, only need to clear the uterus. There may be other reasons for the bleeding even after the injection of low progesterone in pregnancy, you should go to the hospital in time and do the relevant auxiliary examination to determine the cause of the disease before treatment, do not just supplement the progesterone, in order to avoid the delay of the disease, resulting in a bad outcome.