Postpartum dew is the discharge of blood, necrotic membranes and other tissues through the vagina after childbirth with the shedding of the uterine mucosa. There are three stages of changes in the dew, and different stages have different characteristics. The first stage is called bloody nightmare, which occurs within 3-4 days after delivery and is bright red because it contains a large number of blood cells and red blood cells, so it is also called red nightmare clinically; the second stage is plasma nightmare, which contains more plasma fluid and slowly decreases in red blood cells, mainly meconium tissue shed from the endometrium, as well as epidermal cells, a small amount of white blood cells and cervical mucus. The color is light red and lasts for about 10 days; then it slowly turns into white nightmare, the color turns to white, white nightmare contains a lot of white blood cells and some bacteria, shed necrotic uterine mucus and cervical mucus, but contains less red blood cells, so it has a white nightmare shape and is thicker, white nightmare lasts for about 3 weeks. In general, the duration of nightmare lasts about 4-6 weeks.