T2 L13:Prenatal Screening Flashcards
define screening
Screening identifies apparently healthy people who may be at increased risk of a disease or condition, enabling earlier treatment or informed decisions.
what is a HCPS
this scan is a medical test - need to concentrate to take precise measurements
what is the use of the early pregnancy scan
screening for Downs, Edwards, Patau’s syndromes
- First trimester combined test
- second trimester quad test
why scan at 10-14 weeks
-Viability
(2-3% of women attending for scan will have miscarried)
-Accurate dating
(NICE guidance: use scan dates in
lieu of LMP dates
- crucial for screening tests
- reduces need for post dates induction
of labour)
-Detect multiple pregnancy
(determine chjorionicity )
- Diagnosis of structural abnormality (pina bifida
- anencephaly
- exomphalos & gastroschisis
- bladder outflow obstruction)
-Screening for chromosomal conditions ( Down’s -Trisomy 21
Edward’s- Trisomy 18
Patau’s –Trisomy 13)
what is a missed miscarriage
when there are no signs of the baby but the women still fell pregnant
what exactly is Downs syndrome
(occurs at chr 21 because it has a low gene density-237,
via primary translocation/mosaic
there’s an extra chromosome, so extra genes which cause the problems we associate with T21
what are the prenatal diagnosis tests for downs and what are they used for
Chorionic Villus Sampling CVS 11+ weeks
Amniocentesis 16+ weeks
adv: We use screenign tests to work out the chance or likelihood of Downs
disad: 1% chance of miscarriage
what is the difference between a screening test and a diagnostic tests
Screening Tests…
…identify individuals at ‘high’ or ‘low’ chance of having a baby with a trisomy
A low chance result does not exclude trisomy in the baby.
A high chance result does not indicate that the baby is
definitely affected.
No risk of miscarriage
Diagnostic Tests…
…give definitive information on the fetal chromosomes by confirming the presence of an extra chromosome or absence of a chromosome
Risk of miscarriage
Look at slide 17 for pregnancy screening timeline
how was the summary
what is combined in the first trimester screening to determine the chance a baby has T21 13 or 18
(what is the first trimester combined screening )
Maternal age,
Blood test-PAPPA BhCG &
US to determine the amount of fluid behind babies neck (Nuchal translucency scan)
what is the relationship between the maternal age and risk for chromosomal abnormalities
Risk increases with maternal age- increases at faster rate from age 35
What is the purpose of the Nuchal Translucency scan (NT)
determines the amount of fluid behind a babies neck.
its increased in over 80% of t21 cases
87% turners
75% fT18
what is the significance of free beta-HCG and PAPPA-A testing in combined screening for maternal serum biochemical markers
Hcg-lower in downs
PAPPA-A- higher in downs
what are the maternal factors influencing combined screening
Maternal age Gestational age Ethnicity Smoking IVF Multiple pregnancy
what does increased NT (>3.5mm) increase your chances of and so what can you offer as well
- Chromosomal anomaly
- Cardiac anomaly
- ‘Syndromes’
Offer: Karyotyping – array CGH
Fetal cardiac scan
Anomaly scan
what is the second trimester maternal serum screening quadruple test
14+2 to 20 weeks: late bookers only Chance of T21 only Gestational age, maternal age, smoking, weight, ethnicity and … Maternal serum markers: UE3 and AFP -
Inhibin A & BHCG +
what are the detection rates for diff babies
SINGLETONS: DR = 75% SPR = 5.5% TWINS: Monochorionic twins: DR 80% SPR 3% Dichorionic twins: DR 40-50% SPR 3%
what are the options available for mother from the Quad and combined test
1- Do nothing
2- Diagnostic invasive testing [CVS / Amnio]
3- NIPT – non invasive prenatal testing
[not available on NHS
what is CFF DNA
cell free fetal DNA-
CFF DNA is from the placenta so still have risk of placentally confined mosaicism. May also detect a maternal mosaicism or maternal chromosome rearrangement or maternal malignancy.
what is NIPT:
NIPT: Non-invasive prenatal testing Screening for aneuploidy
Cell free fetal DNA [cff DNA] in maternal blood from 5 weeks
Pregnancy specific
Test maternal blood from 10 weeks
Aneuploidy: Screening for T21 sensitivity and specificity over 99%
Marketed as Harmony, SAFE, Panorama, NIFTY test
what are the results from the NIPT and is it offered in UK
Not in NHS as expensive- either 99% chance baby has Downs
1/10000 > chance baby has downs
evaluate NIPT
Advantages
High detection rates, low screen positive rates
Reduction in invasive diagnostic testing [cost effective]
A further option for women
Disadvantages
Screening test: Not diagnostic [false positives / false negatives]
Confirm screen positive results with invasive test
what are options after the condition has been diagnosed
- Continue
- Continue and adoption
- Termination [medical / surgical]
Support- Antenatal Screening Co-ordinator
National support groups:
Antenatal Results and Choices [ARC]
