Group 1 - Down syndrome is a common chromosomal abnormality caused by an extra copy of chromosome 21, leading to congenital intellectual disabilities and various health challenges [2][5] - Characteristics of down syndrome include intellectual developmental delays, physical growth abnormalities, and other health issues such as heart and digestive system problems [3][4][5] Group 2 - Risk factors for down syndrome include advanced maternal age, family history of down syndrome, and chromosomal abnormalities in parents [6] - The risk of having a baby with down syndrome significantly increases for women over 35 years old [6] Group 3 - Common screening methods for down syndrome include early pregnancy screening (11-13 weeks) and mid-pregnancy screening (15-20 weeks), which assess the risk based on maternal blood tests and other factors [7][8] - Diagnostic methods include amniocentesis, chorionic villus sampling (CVS), and non-invasive DNA testing, each with varying levels of risk and accuracy [8] Group 4 - Preventive strategies for reducing the risk of down syndrome include raising awareness of maternal age, genetic counseling, maintaining a healthy lifestyle, and early screening and diagnosis [9][10] - Couples should consider genetic counseling and testing if there is a family history of down syndrome or known chromosomal abnormalities [9]