Antenatal - Downs screening

Question 1

what is the purpose of antenatal screening for Down’s syndrome?

Answer 1

to decide which women should receive more invasive tests to establish a definitive diagnosis. woman’s choice to have screening

Question 2

what are the 3 screening tests done for Down’s syndrome?

Answer 2

Combined test

Triple test

Quadruple test

Question 3

Down’s syndrome screening: what is the combined test and when is it done?

Answer 3

1st line and most accurate screening test done between 11 and 14 weeks

ultrasound - nuchal translucency (DS is 1 cause for NT >6mm)

maternal blood tests - beta-HCG, pregnancy associated plasma protein-A (PAPPA)

Question 4

Down’s screening: what is the triple test?

Answer 4

performed between 12-20 weeks

maternal blood tests:

• beta-HCG - higher = higher risk
• alpha-fetoprotein = lower = higher risk
• serum oestriol - lower = greater risk

Question 5

Down’s screening: what is the quadruple test?

Answer 5

performed between 14 and 20 weeks

identical to the triple test but includes inhibin A

• beta-HCG - higher = higher risk
• alpha-fetoprotein = lower = higher risk
• serum oestriol - lower = greater risk
• inhibin A - higher = greater risk

Question 6

the screenings tests provide a risk score for the fetus having Down’s syndrome. at what risk level are women offered testing? and whats tests are they offered?

Answer 6

risk greater than 1 in 150

offered amniocentesis or chorionic villus sampling (CVS) to take a sample of fetal cells to perform karyotyping

Question 7

Down’s syndrome testing: what is chorionic villus sampling (CVS)

Answer 7

Ultrasound-guided biopsy of placental tissue

used earlier in pregnancy - before 15 weeks

Question 8

Down’s syndrome testing: what is an amniocentesis?

Answer 8

ultrasound guided aspiration of amniotic fluid using a needle and syringe. used later in pregnancy once there is enough amniotic fluid to make it safer to take a sample

Question 9

what is non-invasive prenatal testing (NIPT)?

Answer 9

new test for detecting abnormalities in fetus

sample of maternal blood which will contain fragments of DNA from the placental tissue and represent fetal DNA. these fragments are analysed to detect conditions such as downs

not a definitive test but gives good indication. slowly being rolled out in NHS as alternative to amniocentesis and CVS