When miscarriage occurs after pregnancy (including indolent miscarriage), many patients always ask why? The causes are very complex and mainly include the following: 1. endocrine factors: including gynecological endocrine and endocrine endocrine factors. 2. 2, reproductive system anatomical factors: including congenital anatomical problems and anatomical changes due to acquired diseases. 3, chromosomal problems: including chromosomes of both parents and embryonic chromosomes. 4.Infection factors: including infection of the reproductive tract itself and systemic infectious diseases. 5, immune factors: including autoimmune factors and alloimmune factors. 6, Pre-thrombotic state.