Two types of procedures are available to pregnant women: screening tests and diagnostic tests. The screening tests estimate the risk of the baby having Down syndrome. Diagnostic tests tell whether or not the baby actually has Down syndrome.
At this time the most commonly used screening test is “The Triple Screen.” This is a combination of three tests that measure quantities of various substances in the blood. These tests are usually done between 15 and 20 weeks of gestation.
Sonograms (ultrasounds) are usually performed in conjunction with other screenings. These can show some physical traits that are helpful in calculating the risk of Down syndrome.
Screening tests do not accurately confirm the diagnosis of Down syndrome. In fact, false positives and false negatives frequently occur.
Three diagnostic tests are currently available:
Amniocentesis is performed between 12 and 20 weeks gestation.
Chorionic Villus Sampling (CVS) is conducted between 8 and 12 weeks.
Percutaneous Umbilical Blood Sampling (PUBS) is performed after 20 weeks.