What causes a high risk of trisomy 21?

Trisomy 21, also known as Down syndrome, is a genetic disorder caused by chromosomal abnormalities. A high risk typically indicates an increased likelihood of detecting the presence of this additional chromosome in the fetus through prenatal screening or diagnosis. The main causes of high risk for Trisomy 21 include: 1. Genetic factors: Having a family history of Down syndrome or being a carrier of chromosomal abnormalities may increase the risk of having a child with Down syndrome. 2. Advanced maternal age: As the mother's age increases, the quality of her eggs gradually declines. Older eggs are more prone to errors during cell division, leading to an increased risk of chromosomal abnormalities. 3. Infections during pregnancy: Certain viral infections during pregnancy, such as rubella virus or cytomegalovirus, may adversely affect fetal development and increase the risk of chromosomal abnormalities. 4. Adverse environmental factors: Long-term exposure to harmful substances, radiation, chemicals, and other adverse environmental factors may negatively impact embryonic development, increasing the risk of chromosomal abnormalities. 5. Medical conditions: Pregnant women suffering from certain chronic diseases, such as autoimmune disorders, may have an increased risk of chromosomal abnormalities.