This test is done in the first trimester 9 to 13.4 weeks.Double marker screening or First Trimester Screen is a screening test and not a diagnostic test. This test only tells the risk a mother will have of having a baby with a genetic disorder.In this test two hormonal immunoassay (beta human chorionic gonadotropin (free beta-hCG) and pregnancy-associated plasma protein A (PAPP-A) are quantified and their values are fed in a software along with ultrasound findings and the risk is mathematically calculated. So this test tells us the risk of foetus having any genetic abnormality like Down's syndrome or Trisomy 18 It doesn't give any quantitative value rather a risk factor like 1/250 or 1/1000. It tells us if the report is screen positive or screen negative?.So It just gives the risk whether it is a high risk or low risk.
Now, an enhanced screening is available and is called Dual Marker Plus