Brown fluid on the eleventh day of frozen embryo transfer may be caused by physiological phenomenon or pre-miscarriage. Frozen embryo transfer is a special method of freezing the embryos and then transferring them to the woman’s uterus after thawing and resuscitating them. The fertilized egg may cause a slight shedding of the uterine lining after the transfer. A small amount of brown secretion will flow out of the body. However, if there is insufficient progesterone secretion in the woman’s body after transplantation, she will be prone to the possibility of preeclampsia, which will result in brown vaginal discharge. If there are signs of preeclampsia, you should go to the hospital in time for treatment such as fertility preservation. Early pregnancy should pay more attention to rest, do not strenuous exercise. The first three months can take folic acid, which can play a role in preventing fetal cardiovascular malformation. There may be other reasons for the brown liquid on the eleventh day of frozen embryo transfer, and it is recommended that you go to the hospital in time to get a clear diagnosis and take appropriate treatment for the cause of the disease.