Antenatal testing: Down's syndrome Flashcards
What is now the recommended test for Down’s syndrome?
Combined test
When is the combined test carried out?
11-13+6 weeks
What does the combined test include?
Nuchal translucency measurement
Serum B-HCG
Pregnancy-associated plasma protein A (PAPP-A)
What is Down’s syndrome a result of?
Three copies of chromosome 21- Trisomy 21
What results from the combined test would indicate Down’s syndrome?
↑ HCG
↓ PAPP-A
Thickened nuchal translucency
What other test can be used to diagnose Down’s syndrome?
Quadruple test
When would the quadruple test be offered rather than the combined test?
If a women books later in her pregnancy
When is the quadruple test carried out?
Between 15 - 20 weeks
What does the quadruple test include?
Alpha-fetoprotein
Unconjugated oestriol
Human chorionic gonadotrophin
Inhibin A
What results from the quadruple test would indicate Down’s syndrome?
Decreased alpha-fetoprotein
Decreased unconjugated oestriol
Increased human chorionic gonadotrophin
Increased inhibin A
What type of tests are the combined test and the quadruple test?
Blood tests
What do both the combined and the quadruple test produce?
High chance or low chance result
If a woman has a high chance result, what will she then be offered?
A second screening test (NIPT)
Or
A diagnostic test
What are examples of diagnostic tests?
Chronic villous sampling
Amniocentesis
When can amniocentesis be carried out?
16 weeks onwards (not safe before then)
What is an amniocentesis test?
Removal of amniotic fluid using a fine needle under US
What is the main risk associated with amniocentesis?
Miscarriage (1%)
When can chronic villous sampling be carried out?
10-13 weeks
What does chronic villous sampling involve?
Placenta sampled either transabdominally or transcervically using US
What is the main risk of chronic villous sampling?
Miscarriage
What does NIPT stand for?
Non-invasive prenatal testing
What is tested for in NIPT?
Analyses small DNA fragments that circulate in the blood of a pregnant woman (cell free fetal DNA- cffDNA)
What does cffDNA stand for?
cell free fetal DNA
Is NIPT accuate?
sensitivity and specificity are very high for trisomy 21 (>99%)
