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Screening blood tests include cell-free DNA testing for Trisomy 21, Trisomy 18, and some other chromosomal abnormalities, as well as Early Risk Assessment tests for Trisomy 21 and Trisomy 18. Cell-free DNA detects 99% of babies with Down syndrome, and five percent of patients will have a positive result. A positive screening result does not confirm that the baby has the condition.