Bleeding in early pregnancy and accompanied by shedding of the endometrium is a sign of preterm miscarriage. Under normal circumstances, after pregnancy, a woman’s ovaries will secrete more progesterone. Under the continuous action of progesterone, the proliferated endometrium will turn into secretory phase changes and undergo decidualization to facilitate the fertilized egg’s implantation and development, but decidualization will not occur. Only when the level of progesterone in the body is insufficient to maintain the secretory phase performance of the endometrium as well as the decidualization, will the endometrium shed and cause bleeding. In this case, if progesterone is not supplemented in time for fetal preservation treatment, miscarriage will occur. Once this occurs, if the embryo is developing normally, progesterone supplementation for fetal preservation treatment is needed as soon as possible.