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Module 203, Theme 2- Reproductive System, Fetal Development, Pregnancy and Birth > T2 L13 Prenatal Screening > Flashcards

T2 L13 Prenatal Screening Flashcards

1
Q

What does screening do?

A

Identifies apparently healthy people who may be at increased risk of a disease or condition, enabling earlier treatment or informed decisions

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2
Q

How do healthcare professionals (HCPs) see screening in comparison to parents?

A

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

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3
Q

What are the various public organisations involved in screening? What is their role?

A

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

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4
Q

When is screening carried out?

A

Early pregnancy scan

  • First trimester combined test
  • Second trimester quad test

18+0 – 20+6 weeks fetal anomaly scan

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5
Q

Give examples of chromosomal abnormalities?

A

Down’s syndrome - Trisomy 21
Edward’s syndrome - Trisomy 18
Patau’s syndrome - Trisomy 13

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6
Q

Why is the scan carried out between 10-14 weeks?

A 
Viability
Accurate dating
Detect multiple pregnancy (determine chorionicity)
Diagnosis of structural abnormality
Screening for chromosomal conditions
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7
Q

What % of women attending a scan would have miscarried?

A

2-3 %

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8
Q

What are NICE guidelines for scans?

A

use scan dates in:
- lieu of LMP (last menstrual period) dates
- crucial for screening tests
- reduces need for post dates induction
of labour

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9
Q

Give examples of structural abnormalities?

A
  • spina bifida
  • anencephaly
  • exomphalos & gastroschisis (hole in the abdominal wall)
  • bladder outflow obstruction
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10
Q

Give two example of prenatal diagnostic invasive tests?

A

1) Chorionic Villus Sampling (CVS)

2) Amniocentesis

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11
Q

When does CVS occur?

A

11+ weeks

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12
Q

When does amniocentesis occur?

A

16+ weeks

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13
Q

What is the risk of miscarriage in prenatal diagnostic invasive tests?

A

1%

NOTE: The risk is higher in twins

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14
Q

What does a low chance result in a screening test not exclude?

A

It does not exclude the baby having the condition (e.g. trisomy 21: Down’s syndrome)

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15
Q

What does a high chance result in a screening test not indicate?

A

That the baby will have the condition (e.g Trisomy 13 : Patau’s syndrome

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16
Q

TRUE OR FALSE

There is a risk of miscarriage in screening test

A

FALSE

There is no risk of miscarriage in a screening test

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17
Q

TRUE OR FALSE

There is a risk of miscarriage in a diagnostic test

A

TRUE

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18
Q

What is the aim of a diagnostic test?

A

Give definitive information on the foetal chromosomes by confirming the presence of an extra chromosome or absence of a chromosome.

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19
Q

What week of gestation is the combined screening test carried out?

A

11 (+2) - 14 (+1) weeks

First trimester

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20
Q

What screening methods are used in the combined screening test?

A
  • maternal age
  • amniotic sample
  • maternal blood pressure
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21
Q

What is PAPPA and Beta-hCG? What does it indicate?

A

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

22
Q

What is a Nuchal Translucency Scan (NTS)?

A

Measurement of the fluid at the back of the baby’s neck (nuchal translucency) with an ultrasound scan

23
Q

What happens to the nuchal translucency in babies with Down’s syndrome?

A

It is increased

80% of Down’s syndrome (T21) foetuses have increased nuchal translucency

24
Q

What % of T18 (Edward’s Syndrome) and Turner Syndrome have increased nuchal translucency?

A

75% of T18

87% Turners

25
Q

What is the relationship between the maternal age and the risk of chromosomal abnormalities?

A

As the maternal age increase, the risk of chromosomal abnormalities increase also

26
Q

Is Down syndrome hereditary or random?

A

RANDOM

27
Q

What are the maternal /fetal influencing factors for combined screening?

A

-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

28
Q

What is the cut-off for high/low chance in combined screening?

A

1 in 150

29
Q

What happens if the woman has a higher chance of foetal abnormality (after a combined screening)?

A

They are telephoned within 3 working days

30
Q

What happens if the woman has a lower chance of foetal abnormality (after a combined screening)?

A

They are sent a letter within 2 weeks

31
Q

What is the detection and screen positive rate?

A

Detection rate: 82%

Screen positive rate: 2.7%

32
Q

What risk is increased if the NT> 3.5mm?

A

Increased chance of;

  • Chromosomal anomaly
  • Cardiac anomaly
  • ‘Syndromes’
33
Q

What is offered to women with a foetus that has a NT> 3.5mm?

A
  • Karyotyping – array CGH
  • Fetal cardiac scan
  • Anomaly scan
34
Q

What factors are used in the quadruple screening test?

A
  • gestational age
  • maternal age
  • smoking
  • weight
  • ethnicity

AND

-maternal serum markers

35
Q

What abnormality is tested in the quadruple screening test?

A

ONLY T21 (Down’s syndrome)

36
Q

Which markers are increased/decreased in the quadruple screening test? (maternal serum markers)

A

DECREASED
UE3 (unconjugated E3)
AFP (alpha-fetoprotein)

INCREASED
Inhibin A
BhCG (beta human chorionic gonadotrophin)

37
Q

What are the detection rate for a quadruple test in singletons?

A

SINGLETONS: DR = 75% SPR = 5.5%

NOTE: DR = detection rate, SPR = screen positive rate

38
Q

What are the detection rate for a quadruple test in twins?

A

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

39
Q

What should the HCP do next if there is a higher chance of T13/18/21 on combined or quad screening test?

A

Explain result – reframe the chance: 1 in 50 = 2%]

40
Q

What can the mother do next if there is a higher chance of T13/18/21 on combined or quad screening test?

A

Three main options:
1- Do nothing
2- Diagnostic invasive testing [CVS / Amnio]
3- NIPT – non invasive prenatal testing
[not available on NHS currently]

41
Q

What is non-invasive prenatal screening?

A

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

42
Q

What is the sensitivity and specificity of NIPT in screening for T21 (aneuploidy)?

A

Sensitivity and specificity over 99%

43
Q

Where is the cff DNA from? What risk is associated with the results obtained?

A

The placenta

RISK OF placentally confined mosaicism

44
Q

What is mosaicism?

A

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.

45
Q

Compare the DR & SPR of combined test with NIPT

A

Combined test
SPR 2.7% DR 80%

NIPT
DR > 99%

46
Q

Compare the cost of combined test with NIPT

A

Combined test = just under £20

NIPT = £200

47
Q

Which conditons present a risk of false positive results (in NIPT)?

A
  • Maternal malignancy
  • Multiple pregnancy
  • Blood transfusion within 4 months
  • Organ transplant
  • Vanished twin / demised twin
  • Known chromosome or genetic anomaly in the mother
48
Q

What are the advantages of NIPT?

A

High detection rates, low screen positive rates

Reduction in invasive diagnostic testing [cost effective]

A further option for women

49
Q

What are the disadvantages of NIPT?

A

Screening test: Not diagnostic [false positives / false negatives]

Confirm screen positive results with invasive test

50
Q

What options do women have after T21 is diagnosed on NIPT?

A
  • Continue
  • Continue and give up the baby for adoption
  • Termination [medical / surgical]
51
Q

What support is available to women after T21 is diagnosed on NIPT?

A

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

52
Q

What information is given prior to entering a screening programme?

A
  • 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

Module 203, Theme 2- Reproductive System, Fetal Development, Pregnancy and Birth (17 decks)

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