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MCD Genetics > 5 Prenatal Testing > Flashcards

5 Prenatal Testing Flashcards

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1
Q

Q: What are the normal stages of a pregnancy? (4)

A

A: 1. Positive pregnancy test - does not have to be confirmed at the GP

  1. Booked into antenatal care - see midwife
  2. Nuchal Scan - 10-14 weeks - different tests dependent on the NHS trust
  3. A Mid-Trimester anomaly scan (around 20 weeks)
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2
Q

Q: What is the main method for prenatal diagnosis of foetal abnormalites? Offered?

A

A: Ultrasound examination

All pregnant women should be offered routine ultrasound scans at:

  • 11-14 weeks
  • 20-22 weeks
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3
Q

Q: What occurs during a normal mid-trimester scan?

A

A: -measure long bones

  • measure head diameter
  • do more detailed scans if indicated by family history/defects in previous pregnancy
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4
Q

Q: What are the aims of the 12 week scan? (5)

A

A: (nuchal scan)

  • Date pregnancy
  • detect Multiple Pregnancies
  • detect Major Foetal Abnormalities
  • diagnose Early Miscarriage (no foetal heartbeat)
  • Assess risks of Down Syndrome and other chromosomal abnormalities
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5
Q

Q: How do you assess the risks of Down Syndrome and other chromosomal abnormalities? (6)

A

A: -looking at Nuchal Translucency
-taking into account: maternal age, hormone levels, nasal bone, blood flow through the foetal heart and foetal abnormalities

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6
Q

Q: What is nuchal translucency measured? What is it? What should it be? What can it suggest? (3)

A

A: -10-14 weeks

  • Measure of the fluid at the back of the baby’s neck.
  • usually below 3.5mm // Increased >3mm can indicate:
  1. Chromosome Abnormalities - e.g. Down’s, Patau, Turner, Edwards
  2. Birth Defects: Cardiac Anomalies, Pulmonary Defects (e.g. diaphragmatic hernia), Renal Defects, Abdominal Wall Defects
  3. Skeletal Dysplasia (if long bones aren’t in proportion -> do followups to check if it rectifies or not)
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7
Q

*Q: When is prenatal testing arranged? (5) -indications for referral to genetics services for prenatal genetic testing.

A

A: -Following abnormal findings at nuchal or mid-trimester scan.

  • Following results of combined test which give an increased risk of Down Syndrome.
  • If previous pregnancy affected with a condition e.g. Down Syndrome, Cystic Fibrosis (midwife would refer about this)
  • If the parent(s) is a carrier of chromosome rearrangement or genetic condition e.g. Duchenne Muscular Dystrophy, Huntingdon’s Disease
  • Family History of genetic condition
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8
Q

Q: What are the aims of prenatal testing? (5)

A

A: -inform and prepare parents for the birth of an effected child.

  • In utero treatment could be offered (for some cardiac abnormalities)
  • Aids management of the rest of the pregnancy (extra tests)
  • Allows parents to prepare for complications at or after birth.
  • To allow TERMINATION of an affected foetus
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9
Q

*Q: What are the 3 types of prenatal tests? Include 2 examples for each.

A

A: -Non-Invasive (Ultrasound/MRI which is v detailed)

  • Minimally Invasive (Maternal Blood Test/Cell-Free Foetal DNA)
  • Invasive = go through abdominal cavity -> v accurate (Chorionic Villus Sampling (CVS)/Amniocentesis)
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10
Q

*Q: What are the 3 ultrasound scans during a pregnancy?

A

A: (Non-Invasive Prenatal Tests)

  • Early/dating scan
  • Nuchal Translucency and nasal bone
  • High level/anomaly scan
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11
Q

Q: When is the early/dating scan taken? What does it show?

A

A: from 5 weeks but best from 9 weeks

  • confirms pregnancy
  • see if it’s ectopic
  • or multiple
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12
Q

Q: When is the high level and anomaly scan usually taken? What can it indicate? (4)

A

A: around 20 weeks

  • can be diagnostic - showing cleft lip, limb deformity or cardiac problem
  • It can also show soft markers for other problems
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13
Q

Q: What’s an example of a soft marker? What can this indicate?

A

A: nasal bone

presence or absence can indicate Down Syndrome

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14
Q

*Q: What can foetal MRIs show? (3) When is it taken?

A

A: -how heart and brain are developing

  • what’s happening in abdomen
  • can indicate CF (or other disorders using soft markers)

20+ weeks

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15
Q

Q: What can a foetal cardiac scan show? When are they taken?

A

A: -cardiac problems (looks at bloodflow, heart formation, valve function)
-only done if the other scans indicate potential problem

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16
Q

*Q: Name 2 minimally invasive prenatal tests. What makes them minimall invasive?

A

A: -Maternal Serum Screening
-cell free foetal DNA

These tests involve blood tests for the mum so there is no risk to the foetus.

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17
Q

*Q: What does maternal serum screening involve? What does it detect? Result?

A

A: -tests maternal serum markers in the blood
-detects increased risk of trisomy 21, trisomy 18 and/or neural tube defects

If these tests find that the woman is at high risk of some genetic diseases, she will be offered more invasive prenatal tests

18
Q

*Q: What are the 4 types of maternal serum screening?

A

A: 1st Trimester - 11-14 weeks - done alongside the NT measurement (looks for the presence of hCG (human chorionic gonadotrophin) and PAPP A (pregnancy associated plasma protein A)).

2nd Trimester - 16-20 weeks - done if they are booked in later in pregnancy - looks for hCG and PAPP A and AFP (alpha foetal protein) and uE3 (oestriol).

Nuchal Translucency Measurement - 11-14 weeks

Private - combined 1st and 2nd Trimester Screening available

19
Q

*Q: What is cffDNA? What does a cffDNA test involve? When is a cffDNA test offered? How can trisomy 21 be indicated?

A

A: cfDNA are short DNA fragments and cfDNA in maternal blood comes from both mother and foetus (comes from placenta and is representative of foetal DNA)

  • non invasive prenatal diagnosis works by analysing the DNA fragments present in the maternal plasma during pregnancy
  • currently offered when there is an X-linked condition in the family eg DMD
  • in trisomy 21 the amount of cfDNA for chromosome 21 is higher than in normal pregancy
20
Q

*Q: When cffDNA first detectable? Accurate?

A

A: from 4-5 weeks but is more accurately detected around 9 weeks (usually taken 6-7)

21
Q

*Q: What can cffDNA testing reveal apart from trisomy 21? (3) Cost?

A

A: -achondroplasia
-thanatophoric dysplasia
-apert syndrome
testing is free on the NHS for ^

22
Q

Q: What are the stages to test for DMD?

A

A: test detects SRY gene on Y chromosome-> enabling us to determine if male or female foetus

if male-> go to prenatal test

if female-> don’t as can only be a carrier

23
Q

Q: Which NIPTs are offered privately on the NHS?

A

A: -autosomal dominant single gene disorders inherited from the father or arise de novo eg. NF1 (neurofibromatosis type 1)

24
Q

*Q: Who offers cffDNA testing for aneuploidy? Currently test for? (3)

A

A: private (Harmony) or via research studies

-T13, T18 (97), T21 (99)

92% identified with 13, not that accurate-> room for error

25
Q

*Q: Provide 2 examples of research involved in NIPD?

A

A: -translation of non-invasive prenatal diagnosis (NIPD) for duchenne and becker muscular dystrophy into a clinical setting

-evaluating early NIPD based on cffDNA and RNA in maternal plasma

26
Q

*Q: What are the limitations of NIPD and NIPT? (4)

A

A: Multiple Pregnancies - cannot tell which foetus the DNA is from - only useful if the twins are identical.

High BMI - relative proportions of cffDNA is reduced in women with a high BMI as they have more of their own cell-free DNA.

Ethical Issues - women may not think about the implications of the testing and what results it may give.

An invasive test may still be needed to comfirm

27
Q

*Q: What are the benefits of NIPD and NIPT? (4)

A

A: Reduced number of invasive tests - due to identification of sex

No risk of miscarriage

Less expertise required to perform a blood test

NIPD and NIPT can be offered earlier than invasive tests - results come earlier

28
Q

*Q: When are invasive tests offered? 2 examples. Risk?

A

A: when there is a KNOWN RISK shown by other prenatal testing and if there is a known genetic condition in the family that the baby is at risk of.

  • Chorionic Villus Sampling (CVS)
  • Amniocentesis

of miscarriage

29
Q

*Q: When is Chorionic Villus Sampling (CVS) taken? Risk of miscarriage? Method? Compared to amniocentesis?

A

A: 11-14 weeks

  • 1-2%
  • Transabdominal or Transvaginal : take sample of Chorionic Villus - part of the developing placenta - has the same DNA as the foetus
  • Gives an earlier result than amniocentesis - important for patients deciding on termination of pregnancy
30
Q

*Q: When is Amniocentesis done? Risk of miscarriage? Method? Other risks? (2) Compared to Chorionic Villus Sampling?

A

A: -16+ weeks

  • Up to 1%
  • Takes sample of amniotic fluid which contains foetal cells
  • infection, Rh sensitisation
  • done later
31
Q

*Q: What type of test is done with the DNA sample from CVS or Amniocentesis? (2) What does it depend on? Timing?

A

A: 1. Karyotype - done if there is a chromosomal abnormality in the family / previous pregnancy-> Results in 2 weeks (dependent upon the cells growing)

  1. QF-PCR (Quantitative Fluorescence PCR) where all prenatal samples have a QF-PCR test
    - Test for T13, T18 and T21 (and sex chromosomes if sex chromosome disorder is suspected)
    - Results: 24-48 hours
  • Type of test done depends on the genetic disorder that they are looking for.
  • The timing of the test also depends on the genetic disorder.
32
Q

*Q: If there is a known reproductive risk, the options for having children include what?

A

A: -Conceive naturally - no prenatal testing

  • Conceive naturally - have prenatal testing
  • Egg and/or Sperm Donors
  • Adoption
  • Choose not to have children
  • Pre-implantaion Genetic Diagnosis (PGD)
33
Q

*Q: Anonymity of egg and sperm donation? Done through? (3)

A

A: -No longer anonymous - children conceived have the right to contact the donor when they are 18.

  • Done through UK HFEA licenced fertility centre - conform to strict medical, ethical and legal standards
  • Can find donor privately
  • Some couples may consider going abroad
34
Q

*Q: What are the 2 stages of adoption before a search for a child begins? Include time for first each.

A

A: Registration and Checks

  • Registering interest with adoption agency
  • Medical and Criminal background checks - three written references
  • 2 months roughly

Assessment and Approval

  • Home visits by social workers
  • Prospective Adopters Report is made - taken to adoption panel
  • Panel review the report and make decision about the couple’s suitability to adopt
  • 4 months roughly
35
Q

*Q: What does Pre-implantation Genetic Diagnosis use and involve? Mainly used by? Where is it available? (2)

A

A: Uses IVF but with an extra step - genetically test the embryo before implantation (when there’s 8 cells)

PGD is mainly used by people who aren’t comfortable with terminating the pregnancy

UCH and Guy’s hospital (v expensive)

36
Q

*Q: Describe the process of PGD? (8)

A

A: 1. Stimulation of the ovaries (to produce more eggs)

  1. Eggs are collected (as many as you can)
  2. Insemination - either by IVF (sperm and egg placed together in a culture dish) or ICSI (Intra-Cytoplasmic Sperm Injection - injection of a single sperm into each egg).
  3. Fertilisation
  4. Embryo Biopsy - once embryo gets to about 8 cells in size, a cell is removed by embryo biopsy.
  5. Embryo Testing
  6. Embryo Transfer - embryos that don’t have the genetic condition or are carriers are considered for embryo transfer (maximum 2 are transferred)
  7. Pregnancy Test
37
Q

Q: When is ICSI (Intra-Cytoplasmic Sperm Injection) used?

A

A: for conditions caused by a single gene to reduce the amount of non-embryo DNA (inc sperm DNA) which could make the risk of a wrong diagnosis higer

38
Q

*Q: What is the eligibility criteria for PGD? (6) Licence? Funding?

A

A: -Female partner is under 40

  • Female partner has BMI between 19 and 30
  • Both partners are non-smokers
  • No living unaffected children from the relationship
  • Known risk of having a child affected by a serious genetic condition
  • no welfare concerns for unborn child
  • A licence is required from the HFEA for each genetic condition or indication
  • Eligible couples are usually funded for three rounds of PGD
39
Q

*Q: Name 5 genetic disorders that patients usually use PGD for.

A

A: -translocation errors

  • HD
  • DMD (only implant female embryos where mutation in family is unknown)
  • CF
  • BRCA1/2 (cancer predisposition gene)
40
Q

*Q: What are the problems with PGD? (2) Success rate?

A

A: -Emotional and Physical implications

  • Lengthy process
  • Success Rates: 30% per cycle, 40% per embryo transfer
41
Q

*Q: What’s the role of genetic counselling (GC) in prenatal testing? (6)

A

A: -Arrange and explain the different prenatal tests

  • Facilitate decision-making
  • Give results
  • See patients in clinic following a diagnosis in utero
  • Arrange termination if necessary
  • Discuss recurrence risks and plans for future pregnancies (liase with midwife)
42
Q

*Q: What should be considered when facilitating decision making? (8)

A

A: -Previous experience

  • Family situation
  • Religion
  • Personal beliefs
  • Psychosocial situation
  • Balancing miscarriage risk with genetic risk
  • Dealing with indecision
  • Couples do not always agree

MCD Genetics (7 decks)

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