Chimerism refers to the presence of a population of cells with two or more different chromosome numbers in an individual. Abnormal karyotypes within 10% are considered a low percentage of chimeras. Chimerism is often caused by mitotic nondisjunction to form gamete karyotypes 45, X, 47, XXX, 46, XX, and chromosome loss due to late-stage retardation to form gamete karyotypes 45, X, 46, XX. To confirm the diagnosis of low-proportional chimerism, the patient’s peripheral blood is first taken for lymphocyte culture and chromosomal karyotype analysis. Generally, 5 karyotypes are analyzed first, if there are karyotypes 45, X or 47, XXX, 100 karyotypes are analyzed, if there is one less chromosome and ≥3 karyotypes, or if there is one more chromosome and ≥2 karyotypes, then it is chimerism. 10% or less of the patients are considered to be low-proportional chimerism. Patients with low-proportional chimerism should undergo timely prenatal diagnosis during pregnancy to avoid passing genetic defects to their offspring. For more information, please consult your doctor.