T2 L13 Prenatal Screening Flashcards
What does screening do?
Identifies apparently healthy people who may be at increased risk of a disease or condition, enabling earlier treatment or informed decisions
How do healthcare professionals (HCPs) see screening in comparison to parents?
HCPs: scan is a medical test – need to concentrate to take precise measurements
Parents: Scan is often seen as a social event - - chance to see baby and have photos – bring their family along
What are the various public organisations involved in screening? What is their role?
UK National Screening Committee: makes independent, evidence based recommendations to ministers
Public Health England: exists to protect and improve the nations health and wellbeing and reduce health inequalities.
Develops standards, implements and supports screening policy in collaboration with NHSE.
Quality assures screening [Screening Quality Assurance Service]
NHS England: implements and runs screening services across England
When is screening carried out?
Early pregnancy scan
- First trimester combined test
- Second trimester quad test
18+0 – 20+6 weeks fetal anomaly scan
Give examples of chromosomal abnormalities?
Down’s syndrome - Trisomy 21
Edward’s syndrome - Trisomy 18
Patau’s syndrome - Trisomy 13
Why is the scan carried out between 10-14 weeks?
Viability Accurate dating Detect multiple pregnancy (determine chorionicity) Diagnosis of structural abnormality Screening for chromosomal conditions
What % of women attending a scan would have miscarried?
2-3 %
What are NICE guidelines for scans?
use scan dates in:
- lieu of LMP (last menstrual period) dates
- crucial for screening tests
- reduces need for post dates induction
of labour
Give examples of structural abnormalities?
- spina bifida
- anencephaly
- exomphalos & gastroschisis (hole in the abdominal wall)
- bladder outflow obstruction
Give two example of prenatal diagnostic invasive tests?
1) Chorionic Villus Sampling (CVS)
2) Amniocentesis
When does CVS occur?
11+ weeks
When does amniocentesis occur?
16+ weeks
What is the risk of miscarriage in prenatal diagnostic invasive tests?
1%
NOTE: The risk is higher in twins
What does a low chance result in a screening test not exclude?
It does not exclude the baby having the condition (e.g. trisomy 21: Down’s syndrome)
What does a high chance result in a screening test not indicate?
That the baby will have the condition (e.g Trisomy 13 : Patau’s syndrome
TRUE OR FALSE
There is a risk of miscarriage in screening test
FALSE
There is no risk of miscarriage in a screening test
TRUE OR FALSE
There is a risk of miscarriage in a diagnostic test
TRUE
What is the aim of a diagnostic test?
Give definitive information on the foetal chromosomes by confirming the presence of an extra chromosome or absence of a chromosome.
What week of gestation is the combined screening test carried out?
11 (+2) - 14 (+1) weeks
First trimester
What screening methods are used in the combined screening test?
- maternal age
- amniotic sample
- maternal blood pressure
What is PAPPA and Beta-hCG? What does it indicate?
Pregnancy-associated plasma protein A (PAPPA)
-Women with low blood levels of PAPPA at 8 to 14
weeks of gestation have an increased chance of
their baby having Trisomy 21 and/or Trisomy 13/18
Beta Human chorionic gonadotropin (beta-hCG)
-Used to diagnose pregnancy. Beta-hCG is higher
than average in Down’s syndrome
What is a Nuchal Translucency Scan (NTS)?
Measurement of the fluid at the back of the baby’s neck (nuchal translucency) with an ultrasound scan
What happens to the nuchal translucency in babies with Down’s syndrome?
It is increased
80% of Down’s syndrome (T21) foetuses have increased nuchal translucency
What % of T18 (Edward’s Syndrome) and Turner Syndrome have increased nuchal translucency?
75% of T18
87% Turners
What is the relationship between the maternal age and the risk of chromosomal abnormalities?
As the maternal age increase, the risk of chromosomal abnormalities increase also
Is Down syndrome hereditary or random?
RANDOM
What are the maternal /fetal influencing factors for combined screening?
-Maternal age
-Gestational age
-Ethnicity
-Smoking
-IVF (the hormones given can influence the marker
levels in the blood)
-Multiple pregnancy
-Weight (higher weight can affect the marker levels in
the blood)
-Diabetes
-Past history of chromosome abnormality
-Fetal sex
-Analytical Imprecision
What is the cut-off for high/low chance in combined screening?
1 in 150
What happens if the woman has a higher chance of foetal abnormality (after a combined screening)?
They are telephoned within 3 working days
What happens if the woman has a lower chance of foetal abnormality (after a combined screening)?
They are sent a letter within 2 weeks
What is the detection and screen positive rate?
Detection rate: 82%
Screen positive rate: 2.7%
What risk is increased if the NT> 3.5mm?
Increased chance of;
- Chromosomal anomaly
- Cardiac anomaly
- ‘Syndromes’
What is offered to women with a foetus that has a NT> 3.5mm?
- Karyotyping – array CGH
- Fetal cardiac scan
- Anomaly scan
What factors are used in the quadruple screening test?
- gestational age
- maternal age
- smoking
- weight
- ethnicity
AND
-maternal serum markers
What abnormality is tested in the quadruple screening test?
ONLY T21 (Down’s syndrome)
Which markers are increased/decreased in the quadruple screening test? (maternal serum markers)
DECREASED
UE3 (unconjugated E3)
AFP (alpha-fetoprotein)
INCREASED
Inhibin A
BhCG (beta human chorionic gonadotrophin)
What are the detection rate for a quadruple test in singletons?
SINGLETONS: DR = 75% SPR = 5.5%
NOTE: DR = detection rate, SPR = screen positive rate
What are the detection rate for a quadruple test in twins?
TWINS:
Monochorionic twins:
DR 80% SPR 3%
Dichorionic twins (there are 4 possible outcomes. Both may have Down’s, baby A or B may have Down’s and none of them have Down’s): DR 40-50% SPR 3%
NOTE: DR = detection rate, SPR = screen positive rate
What should the HCP do next if there is a higher chance of T13/18/21 on combined or quad screening test?
Explain result – reframe the chance: 1 in 50 = 2%]
What can the mother do next if there is a higher chance of T13/18/21 on combined or quad screening test?
Three main options:
1- Do nothing
2- Diagnostic invasive testing [CVS / Amnio]
3- NIPT – non invasive prenatal testing
[not available on NHS currently]
What is non-invasive prenatal screening?
It test cell free foetal DNA in the maternal blood from 10 weeks
Cell free fetal DNA [cff DNA] is present in the maternal blood from 5 weeks
This test is pregnancy specific
NOTE: It is marketed as Harmony, SAFE, Panorama, NIFTY test
What is the sensitivity and specificity of NIPT in screening for T21 (aneuploidy)?
Sensitivity and specificity over 99%
Where is the cff DNA from? What risk is associated with the results obtained?
The placenta
RISK OF placentally confined mosaicism
What is mosaicism?
Involves the presence of two or more populations of cells with different genotypes in one individual who has developed from a single fertilized egg.
Mosaicism has been reported to be present in as high as 70% of cleavage stage embryos and 90% of blastocyst-stage embryos derived from in vitro fertilization.
Compare the DR & SPR of combined test with NIPT
Combined test
SPR 2.7% DR 80%
NIPT
DR > 99%
Compare the cost of combined test with NIPT
Combined test = just under £20
NIPT = £200
Which conditons present a risk of false positive results (in NIPT)?
- Maternal malignancy
- Multiple pregnancy
- Blood transfusion within 4 months
- Organ transplant
- Vanished twin / demised twin
- Known chromosome or genetic anomaly in the mother
What are the advantages of NIPT?
High detection rates, low screen positive rates
Reduction in invasive diagnostic testing [cost effective]
A further option for women
What are the disadvantages of NIPT?
Screening test: Not diagnostic [false positives / false negatives]
Confirm screen positive results with invasive test
What options do women have after T21 is diagnosed on NIPT?
- Continue
- Continue and give up the baby for adoption
- Termination [medical / surgical]
What support is available to women after T21 is diagnosed on NIPT?
Antenatal Screening Co-ordinator
National support groups:
- Antenatal Results and Choices [ARC] - Downs syndrome association [DSA] - Soft U.K. [Tri 13 and 18], Unique, Contact-A-Family
Meet other parents [Specialist Health Visitor / local groups]
Obstetric / neonatal / paediatric teams
Genetic counselling
What information is given prior to entering a screening programme?
- Tests are optional
- What are we screening for?
- What the test will not tell you
- Timing of tests
- Communicating results – higher / lower chance
- Invasive tests [miscarriage rate]
- Options if abnormality diagnosed
- Contact for further advice
