Genetic Screening Flashcards
Combined first trimester test
US to measure foetal nuchal translucency 11-13+6/40
+
Maternal plasma testing for PAPP-A (pregnancy-associated placental protein-A), free bHCG
- Blood test performed 9/40-13+6/40
NIPT
Non-invasive prenatal testing
- Performed from 10/40
- Sequencing DNA fragments in maternal serum, mapping each DNA sequence to a reference genome to determine its chromosome of origin.
- Number of fragments is counted
- If foetus is affected by trisomy, a greater than expected number of relevant chromosome fragments will be present in maternal serum.
Note: Still offer 11-13/40 US for early structural assessment, as 50% of major abnormalities can be detected at this gestation.
Triple Test
Genetic screening later in pregnancy.
14-20/40
- AFP, free bHCG, unconjugated oestriol
Useful for
- later presentation of pregnant women
- No availability of specialist obstetric ultrasound
- Unable to afford NIPT
Quadruple Test
Genetic screening later in pregnancy.
14-20/40
- AFP, free bHCG, unconjugated oestriol, Inhibin A
Useful for
- later presentation of pregnant women
- No availability of specialist obstetric ultrasound
- Unable to afford NIPT
Chorionic villus sampling
Diagnostic test
- 10-13/40
- Delayed until 10/40 to avoid sampling in spontaneous pregnancy loss and also to reduce risk of limb-reduction defects
Amniocentesis
Diagnostic test
- 15/40 but normal > 16/40
Screening Test Explanation
- Screening test to determine who is at increased risk of having a baby with a chromosomal
condition
Examples of screening genetic tests include
- CFTS
- NIPT
- Triple test
- Quadruple test
- Mothers will be offered invasive diagnostic testing if they receive a high-risk screening.
- CVS
- Amniocentesis
- No increased risk of miscarriage from screening tests.
- Low-risk results do not exclude the possibility of a chromosomal abnormality.
