Down's Syndrome Antenatal Screening

Question 1

What is the timeline for Down’s Syndrome antenatal screening?

Answer 1

11-14 weeks gestation: Combined tests - Ultrasound + beta HCG and PAPPA blood test

14-20 weeks gestation: Triple test - Beta HCG, Alpha fetoprotein, oestriol

14-20 weeks gestation: Quadruple test - same as triple test but also includes inhibin A test

= if risk score from these tests is greater than 1/150, offer amniocentesis/chorionic villus sampling

Before 15 weeks: chorionic villus sampling
Later in pregnancy: amniocentesis

Non invasive prenatal testing

Question 2

What does the combined test measure?

Answer 2

Ultrasound - nuchal translucency greater than 6mm = greater risk of Down’s

Beta HCG - high result = greater risk
PAPPA - lower result = greater risk

Question 3

What does the triple test for Down’s measure?

What does the quadruple test measure?

Answer 3

Beta HCG - high result = greater risk
Alpha fetoprotein - lower result = greater risk
Serum oestriol - lower result = greater risk

Quadruple test tests for the same above, but also inhibin A - if high = greater risk