What are the typical prenatal tests to check for down syndrome? what week of pregnancy do they typically test for this?

Integrated Prenatal: Screening determines risk of Down Syndrome or other Trisomies, calculated from findings on 1st & , often, 2nd trimester Fetal Ultrasounds, 1st & 2nd trimester specific maternal blood tests + gestational & maternal age, so parents can decide if they want a diagnostic test for analysis of fetal chromosomes. See http://www.womenandinfants.org/pdc/integrated-screening-test for specific markers.