First Trimester Combined Screen (FTCS)
Two tests (a nuchal test and a blood test) are used to estimate the chance of having a baby with Down syndrome, Trisomy 18, or Trisomy 13. The detection rate for FTCS is around 75-90% with a false positive rate of around 3-9% (GECKO).
- Nuchal translucency test. This is an ultrasound that measures the thickness of the area at the back of the baby’s neck. A larger measurement is associated with an increased likelihood of chromosome conditions like Down syndrome and other genetic conditions, or non-genetic issues like congenital heart defects. The nuchal ultrasound test is done between 11 and 13 weeks 6 days of pregnancy and is not available everywhere as it should be done at a certified site.
- Maternal blood test. Done after the ultrasound, the maternal blood test measures two hormones: beta human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein A (PAPP-A). Combined with the ultrasound results, the levels are used to determine a higher or lower likelihood of specific concerns in the pregnancy.
Quadruple Screen (“Quad” screen, or Maternal serum screen)
This is a blood test performed between 15 weeks to 20 weeks 6 days of pregnancy, which looks for four different proteins circulating in the maternal blood. It assesses for conditions such as Down syndrome, Trisomy 18, and open neural tube defects. It gives a detection rate for Down syndrome of around 80%, with 5% false positives, meaning that around 20% of affected pregnancies are missed by this test (reference: GECKO).
A good source of information for prenatal screening can be found at GECKO (Genetics Education Canada- Knowledge Organization): A guide to understanding prenatal screening tests. http://geneticseducation.ca/public-resources/prenatal-and-preconception-genetics/guide-to-understanding-prenatal-screening-tests/
Note that integrated prenatal screening (IPS) and Serum integrated prenatal screening (SIPS) are not available in Alberta.