Double Marker Test

**Semantic type:** Laboratory Procedure

**Definition:** A blood test done near the end of the first trimester of pregnancy to screen for common chromosomal defects. This test screens for blood levels of both free beta-human chorionic gonadotrophin (beta-hCG) and pregnancy-associated plasma protein A (PAPP-A) and can detect trisomies of chromosomes 21 (Down's syndrome), chromosome 18 (Edward's syndrome), and chromosome 13 (Patau's syndrome).

**Synonyms:** - Double Screen - Double test