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GENETICS my version > Genetic Testing > Flashcards

Genetic Testing Flashcards

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1
Q

what 2 scans are done in normal pregnancoies?

A
  1. Nuchal scan
  2. mid-trimester anomaly scan

both of these are ultrasounds

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2
Q

When is a nuchal scan done?

A

10-14 weeks gestation

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3
Q

What 5 things can a Nuchal Scan do?

A
  1. date the pregnancy
  2. diagnose multiple pregnancies
  3. disgnose major fetal abnormalities
  4. diagnose early miscarriage
  5. assess the risk of down syndrome
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4
Q

What technique is used to assess the risk of down syndrome?

A

Nuchal translucency scan

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5
Q

At how many weeks is a mid trimester scan done?

A

20-22 weeks

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6
Q

What is the purpose of the mid trimester anomaly scan?

A

To take a more detailed lookat specific organs like heart, brain, spinal cord and to check for 11 rare conditions

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7
Q

What is measured during a Nuchal Translucency test?

A

The thickness of fluid at the back of the foetal neck

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8
Q

A nuchal translucency if more than how many mm indicates a problem?

A

anything more than 3mm

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9
Q

If the nuchal thickness is >3mm, what can it indicate?

A

chromosome abnormalities such as down syndrome

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10
Q

What birth defects can arise from an increase nuchal translucency? d

A
  1. Cardiac abnormalities
  2. Pulmonary abnormalities
  3. Renal defects
  4. Abdominal wall defects
  5. Skeletal dysplasias
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11
Q

What is linked to nuchal translucency which increases the risk of the baby having down synrdome?

A

Maternal age

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12
Q

Sometime we see increased NT but there’s nothing actually wrong with the baby. Why is this?

A

as this is just a screening test and not diagnostic

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13
Q

What type of test is a nuchal translucency scan?

A

A screening test

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14
Q

Give some examples when prenatal testing could be offered?

A
  1. Abnormal findings in nuchal scan or mid-trimester
  2. If the couple had an affected child in previous pregnancies
  3. if parents are carriers of severe genetic conditions
  4. family history of genetic conditions
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15
Q

What are the 4 main aims of prenatal testing?

A
  1. Inform / prepare parents
  2. Allow for the termination of pregnancy if necessary
  3. Help manage the remainder of the pregnancy
  4. to be prepared for complications at or after birth
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16
Q

When is the 1st trimester maternal serum screening and NT measurement done at?

A

11-14 weeks

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17
Q

what is cell-free fetal DNA (cffDNA)

A

DNA that shed from placenta +into the maternal blood

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18
Q

What does cell free foetal DNA screening do?

A

Analyses the placental DNA in maternal plasma

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19
Q

When is cffDNA first ever detectable?d

A

4-5 weeks gestation

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20
Q

how can cffDNA be used in non-invasive screening/diagnosis techniques?

A
  1. NIPD
  2. NIPD fetal sexting
  3. NIPT
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21
Q

When is the Cell-Free Foetal DNA reading most accurate?

A

9 weeks

22
Q

what is NIPT?

A

cfff DNA testing for aneuploidy
this is testing not diagnostic

23
Q

what aneuplodies does NIPT test for?

A

T13
T18
T21

24
Q

What gene is detected on the Y chromosome in sexting tests?

A

The SRY gene = males

25
Q

In what instance is sexting offered?

A

when there is an X-linked condition in the family - males more at risk so if the baby is male, then go on to pre natal tests to double check

26
Q

what are the major limitations of NIPD + NIPT?

A
  • cannot be used in
    1. multiple pregnancies
    2. women w high bmis
    3. women not prepared for implications
    3. may still need invasive test to confirm result
27
Q

What are the two types of invasive tests required?

A

Amniocentesis and Chorionic Villus Sampling

28
Q

Where are the chorionic villi found?

A

As part of the developing placenta

29
Q

Why is a sample of the chorionic villi taken to check for genetic conditons?

A

It has the same DNA as foetus

30
Q

Why is CVS chosen over amniocentesis?

A

It allows the parents to have their results earlier than amnio

31
Q

When is CVS done?

A

11-14 weeks, usually at 12

32
Q

How are CVS samples taken?

A

Transvaginally or transabdominally

33
Q

At what stage is amniocentesis done at?

A

from 16 weeks

34
Q

What does amniocentesis involve?

A

Sample of amniotic fluid is taken as it contains foetal cells

35
Q

What are the 3 risks associated with Amniocentesis?

A
  1. Rh sensitisation
  2. Miscarriage
  3. Infection
36
Q

What happens to cffDNA in women with a higher BMI?

A

Lower cffDNA count as they have more of their own DNA

37
Q

What is the limitation of non-invasive prenatal tests involving twins?

A

not possible to tell which foetus the DNA is from

38
Q

What are the benefits of non-invasive pre-natal testing over invasive techniques

A
  1. No risk of miscarriage
  2. Less impactful on the baby / mother
  3. Less expertise is needed to perform the tests
  4. Can be done earlier han invasive techiques
39
Q

what tests can be done w DNA sample from invasive techniques?

A
  1. Test for specific genetic disorder
  2. can karyotype it
  3. QF- PCR
40
Q

What is the purpose of a CGH array?

A

looks for imbalances in chromosomes that may lead to diseases

41
Q

What may be done after a CGH array if chromosomal imbalances are found?

A

Testing of parents to see if they are carriers

42
Q

What is a prenatal exome test?

A

A full genetic sequencing

43
Q

When are prenatal exome tests offered?

A

considered when fetus has significant anomalies e.g heart, brain, skeletal

44
Q

how quick do the results come from prenatal exome tests?

A

approx. 1 week

45
Q

what are the reproductive options?

A
  1. conceive naturally, no prenatal testing
  2. conceive naturally + prenatal testing
  3. use egg/sperm donors
  4. Adoption
  5. Dont have kids
  6. Pre-implantation genetic diagnosis
46
Q

what is pre-implantation genetic diagnosis (PDG)?

A

specialised form of IVF with an additional step to genetically test the embryo b4 implantation

47
Q

when is pre-implantation genetic diagnosis used?

A

For conditions caused by single faulty gene to reduce the amount of non-embryo DNA (including sperm DNA) which could make the risk of a wrong diagnosis higher

48
Q

At what stage is the embryo biopsied?

A

8 cell stage

49
Q

what is the eligibilit criteria for PGD?

A
  • female must be under 39
    have a healthy bmi
    both partners=non smokers
    couple in a stable relationship
    no living unaffected child
    known risk of having a child w a serious genetic condition
50
Q

What are the downsides of PIGD?

A
  1. Can be emotionally stressful
  2. Lengthy and expensive process
  3. Success rate is low - around 30% per cycle
51
Q

How many rounds of PIGD are couples usually funded for provided they fit the criteria?

A

3

52
Q

What is the role of a genetic counsellor in prenatal testing?

A
  1. Arrange CVS and amnio
  2. Provide emotional support for parents
  3. Provide information on termination options
  4. Facilitate decision making
  5. give results of tests
  6. Discuss recurrence risks and plans for future pregnancies

GENETICS my version (9 decks)

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