Brown secretion on the sixth day of blastocyst transfer may be caused by bleeding on implantation, preeclampsia and so on. 1. Bleeding on implantation: after blastocyst implantation, when the embryo implantation due to endometrial breakthrough bleeding, some people may show vaginal bleeding, this kind of bleeding is generally very small amount, the bleeding time is also very short, and it will disappear very soon, and women do not need to worry. 2. Pre-eclampsia: If the embryo is unstable due to poor embryonic development and maternal hormone insufficiency after the blastocyst has been placed in the bed, symptoms of pre-eclampsia such as vaginal bleeding may occur, and women need to take bed rest while insisting on the use of hormonal support. Attention should also be paid to checking progesterone and blood HCG, if the level is low and the bleeding gradually increases, the transfer may fail. Brown discharge on the sixth day of blastocyst transfer requires prompt medical examination and treatment as prescribed.