Fluid buildup on b ultrasound at 28 days of transfer may be caused by preeclampsia, subchorionic hematoma and other reasons. 1. Pre-eclampsia: Transfer refers to the in vitro fertilization-embryo transfer technique, which has to be operated by a specialized physician. Ultrasound is done at 28 days after embryo transfer to clarify that it is an intrauterine pregnancy. When symptoms of preeclampsia such as lower abdominal pain and vaginal bleeding are present, ultrasound may indicate the presence of uterine fluid, which is also combined with progesterone and blood HCG (human chorionic gonadotropin) levels to assist in the diagnosis. 2. Subchorionic hematoma: also manifested as lower abdominal pain, vaginal bleeding and other symptoms, ultrasound suggests that there is fluid in the uterine cavity, is due to the separation of the chorionic plate and the bottom of the metaplasia of the pregnancy and the hemorrhage, need to be combined with the progesterone, transaminase, homocysteine, D-dimer and anticardiolipin antibodies, antinuclear antibodies and other laboratory tests to assist in the diagnosis. The presence of fluid on ultrasound at 28 days after transplantation can be identified and treated aggressively under the supervision of a physician.