The presence of membrane-like stuff in menstrual blood is normal and is a fragment of necrotic shed endometrium. Menstruation is the regular bleeding of the endometrium under the action of estrogen. The main components are water, blood cells, endometrial debris, and a small amount of microorganisms. The normal endometrium is white in color and may appear red or dark red because it is mixed with blood. Under normal circumstances, the endometrium begins to proliferate under the action of estrogen after menstruation and reaches about 8-13 mm during ovulation. The estrogen in the body reaches a high level before menstruation, and then the estrogen suddenly drops, causing the endometrium to lose hormonal support for shedding and bleeding followed by menstruation. There are large and small endometrial fragments in menstrual blood. Larger fragments are visible to the naked eye, while smaller fragments are mixed in menstrual blood and are not easily detected.