The causes of chromosomal abnormalities in embryos mainly include genetic factors, environmental influences, and abnormal sperm and egg formation. 1. Genetic factors: both parents have chromosomal abnormalities, then chromosomal abnormalities may be inherited to the next generation. 2. Environmental factors: the first three months of pregnancy is a highly sensitive period for fetal malformations, and if you are affected by food, environment, viruses, drugs, etc., such as home renovation, viral infections, food pesticide residues, etc., you may increase the risk of chromosomal abnormalities. 3. Abnormal sperm and egg formation process: abnormal development of fertilized eggs, such as advanced maternal age in the formation of the egg, if chromosome 21 has not been successfully split, the sperm and egg combination leads to three chromosome 21, which will result in trisomy 21 abnormalities. Chromosomal abnormalities have more causes, couples should improve chromosome examination, avoid toxic and harmful environments, and maintain a good state of mind.