The normal duration of maternal malignant dew is three weeks and 21 days, the first two weeks should be bloody malignant dew, and the last week is plasma malignant dew, which is a yellowish-brown discharge, etc. If new blood appears more than 20 days after delivery, the following points should be considered: 1. Is there placenta or fetal membrane residue? If necessary, routine blood tests should be performed. 3. Few people can resume normal menstrual cycle about one month after delivery. So at this time, if there is no abnormality as mentioned before, you can also observe for a few days to see if the blood is clean by itself.