Brown discharge after seeing red at 16 weeks of pregnancy may be the manifestation of lesions caused by various pathogenic factors such as preeclampsia, placenta hypoplasia and embryonic arrest. 1. Pre-eclampsia: at 16 weeks of pregnancy, if a pregnant woman is stimulated by various pathogenic factors such as emotional factors, life factors, environmental factors, external factors, etc., it may cause uterine contractions inducing pre-eclampsia, and the pregnancy sac is slightly separated from the uterine wall, which may lead to the sighting of redness, and the blood is mixed with secretions to be discharged, and then brown secretions will appear. 2. Placenta hypoplasia: If the placenta is low in the 16th week of pregnancy, near the endocervix, uterine contractions may lead to separation of the placenta from the uterine wall, which may lead to redness caused by brown discharge. 3. Embryonic arrest: in the 16th week of pregnancy, if the embryo has chromosomal developmental abnormalities caused by embryonic arrest, the embryo and its affiliated tissues out of the uterine cavity, there may be brown discharge after seeing red. The causes of brown discharge after seeing red at 16 weeks of pregnancy are more varied and need to be treated appropriately under the guidance of a medical professional.