Fetal arrest around 50 days of pregnancy may be caused by the embryo itself, the mother, the environment and so on. 1. Embryo’s own reasons: chromosomal abnormality of embryo is the most common reason for the occurrence of fetal arrest, mostly seen in chromosome number abnormality, such as trisomy 21, trisomy 18, trisomy 13 and so on, as well as chromosome structural abnormality, such as equilibrium translocation, deletion, inversion and so on. 2. Maternal causes: (1) Systemic diseases: such as hyperthermia, severe infections, severe anemia and thrombophilia, etc., may lead to fetal arrest. (2) Abnormal immune function: including abnormal autoimmune function, such as antiphospholipid antibody and lupus anticoagulant factor-positive people, etc., as well as abnormal homozygous immune function, such as excessive compatibility of human cellular antigens of both husband and wife, which can result in the lack of closure factor or abnormally high number or activity of natural killer cells. (3) endocrine abnormalities: such as luteal insufficiency, hypothyroidism, diabetes mellitus poor glycemic control, hyperprolactinemia, etc., may also lead to fetal arrest. 3. Environmental causes: when exposed to excessive formaldehyde, benzene, ethylene oxide and other chemicals during pregnancy, it may also cause fetal arrest. You need to go to the hospital in time to find out the cause and treat it actively when the pregnancy stops around 50 days.