The black discharge on the 11th day of frozen embryo transplantation may be caused by the implantation of the fertilized egg, preeclampsia, and uterine effusion. 1. Fertilized egg implantation: In the process of implantation, the fertilized egg may cause stimulation to the endometrium, causing a small amount of bleeding, due to the relatively small amount of bleeding, discharge time is relatively late, and will be manifested as black discharge. 2. Pre-eclampsia: after the transfer of frozen embryos, if there is a phenomenon of corpus luteum insufficiency, it is easy to lead to pre-eclampsia, the bleeding is relatively small, and there will be a black secretion discharged through the vagina. 3. Uterine fluid: in the transfer of frozen embryos to the uterine cavity, there may be damage to the capillaries, rupture, if the amount of bleeding is relatively small, it will cause the uterine fluid outflow will be manifested as black secretion phenomenon. Transfer frozen embryo 11 days to black discharge, it is recommended to go to the hospital in a timely manner, for relevant projects, in the doctor’s interview with the relevant projects, combined with the examination, to clarify the cause of the disease, targeted treatment.