Screening for Down Syndrome

Why is the American College of Obstetrics and Gynecologists recommending that every pregnancy be screened towards the end of the first trimester for the possibility of the unborn child having Down Syndrome? Why do they want the test taken before the 20th week of gestation?

The term "search and destroy" seems to work here. I'm not seeing any guidelines calling for improving the counseling of parents who receive whose unborn child's test comes back positive for Down Syndrome. What will the false positive rate be for these tests? How many parents will abort their unborn child because they think she has Down Syndrome when she doesn't?

The Wikipedia page for Down Syndrome notes that the false positive rate for the Nuchal translucency/free beta/PAPPA screen is 5% and one systematic literature review found that around 92% of pregnancies where there was a prenatal diagnosis for Down Syndrome ended in abortion.

Tags: down syndrome, unborn, abortion