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Human Reproduction > Prenatal diagnosis > Flashcards

Prenatal diagnosis Flashcards

1
Q

What factors determine a high risk pregnancy?

A
  1. Family history of genetic disease
  2. Maternal illness
  3. History of abnormal pregnancy
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2
Q

What is the main contributing factor to neural tube defects?

A

Folic acid deficiency

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3
Q

How are open neural tube defects detected?

A
  1. Ultrasound
  2. Elevated levels of α-fetoprotein in maternal serum
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4
Q

How are chromosome defects detected?

A
  1. Aneuploidy (loss/gain of whole chromosome): Cytogenetics (e.g. karyotyping [analysis under microscope])
  2. Translocations:
    - Large: Cytogenetics
    - Small: Microarray
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5
Q

What causes Down’s syndrome?

A

Trisomy 21

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6
Q

What are the symptoms of Down’s syndrome?

A
  1. Intellectual impairment
  2. Craniofacial abnormalities (e.g. flat nasal bridge, slanting palpebral fissure…)
  3. Single palm crease
  4. Cardiac defects
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7
Q

What causes Edward syndrome?

A

Trisomy 18

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8
Q

What are the symptoms of Edward syndrome?

A
  1. Intellectual impairment
  2. Craniofacial abnormalities (e.g. micrognathia)
  3. Clenched overlapping fingers
  4. Prominent heels
  5. Rocker-bottom feet
  6. Cardiac defects
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9
Q

What causes Patau syndrome?

A

Trisomy 13

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10
Q

What are the symptoms of Patau syndrome?

A
  1. Intellectual impairment
  2. Craniofacial abnromalities (e.g. cleft palate, cleft lip, holoprosencephaly)
  3. Renal abnormalities
  4. Cardiac defects
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11
Q

What are the types of aneuploidies?

A
  1. Down’s syndrome - Trisomy 21
  2. Edward syndrome - Trisomy 18
  3. Patau syndrome - Trisomy 13
  4. Turner syndrome - XO
  5. Kleinfelter’s syndrome - XXY
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12
Q

What are the purposes of the “Early pregnancy scan”, or ‘booking scan’?

A
  1. Determination of gestational age:
    - Foetal crown rump length (length from top of head to buttock)
    - Bi-parietal diameter (diameter of head in coronal plane)
  2. Viability assessment
  3. Number of foetuses (multiple pregnancy)
  4. Detection of severe congenital abnormalities
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13
Q

What type of scan is the early pregnancy scan?

A

Ultrasound scan

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14
Q

When is the early pregnancy scan performed?

A

Before 15 weeks

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15
Q

What is nuchal translucency thickness?

A

Thickness of collection of fluids behind neck of foetus

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16
Q

What can increased nuchal translucency thickness be an indicator for?

A
  1. Down’s syndrome
  2. Congenital heart defects
  3. Venous congestion in head and neck due to constriction of foetal body
  4. Abnormalities in lymphatics system
  5. Neuromuscular disorders leading to impaired foetal movements
  6. Foetal anaemia/hyoproteinaemia
  7. Congenital infections due to anaemia/cardiac defects
17
Q

What is the purpose of the foetal anomaly scan?

A

Confirm absence of foetal anomalies or to identify present anomalies. These include anomalies that are:

  1. Not compatible with life
  2. Associated with high risk of mortality/morbidity
  3. Conditions that may be treated pre-natally
  4. Conditions that need to be treated post-natally
18
Q

When does anencephaly become visible?

A

10-14 weeks

19
Q

When does spina bifida become visible?

A

16-22 weeks

20
Q

What are the indirect markers for neural tube defects?

A
  1. Lemon sign (transverse plane): Indentation of frontal bone resulting in lemon shape of skull.
  2. Banana sign (transverse plane): Tight wrapping of cerebellum around brainstem results in banana-like appearance.
21
Q

Where is α-fetoprotein produced and how does it enter maternal circulation?

A

Production:

  1. Liver
  2. Yolk sac

Entry into circulation:

  1. Directly across placenta
  2. Indirectly from amniotic fluid via uterine decidua
22
Q

How is α-fetoprotein levels measured?

A

Immunoassay (e.g. ELISA)

23
Q

What is the importance of gestational age in prenatal diagnosis?

A

Levels of different serum markers differ throughout gestation and so accurate estimate of gestational age needed to interpret data.

24
Q

What is measured in the Triple test?

A
  1. α-fetoprotein (AFP)
  2. Unconjugated estriol (μE3)
  3. Human chorionic gonadotrophin (hCG)
25
Q

What are the invasive prenatal diagnosis techniques?

A
  1. Chorionic villous sampling
  2. Amniocentesis
  3. Foetal blood sampling
  4. Foetoscopy
    - Foetal skin biopsy
26
Q

What are the non-invasive prenatal diagnosis techniques?

A
  1. Ultrasound
  2. Free foetal DNA in maternal blood
27
Q

What is chorionic villous sampling (CVS) and what are the associated risks?

A

Method:

  • Carried out between 11-14 weeks
  • Needle penetrates placenta to take sample of trophoblast cells
  • Sufficient DNA for analysis without cell culturing needed

Risk: Infection & 1-2% miscarriage

28
Q

What is amniocentesis and what are the associated risks?

A

Method:

  • Carried out between 15-20 weeks
  • Needle passed into amnion transabdominally under ultrasound guidance
  • Fluid sample removed
  • Foetal cells need at least 2 weeks to culture

Risk: Infection & 0.5% miscarriage

29
Q

What are the advantages and disadvantages of CVS?

A

Advantages: Early diagnosis (no cell culturing)

Disadvantages:

  • High risk of miscarriage
  • Use of extraembryonic tissue and so less representitive (due to placental mosaicism)
30
Q

What are the advantages and disadvantages of amniocentesis?

A

Advantages:

  • Foetal material so is more representitive
  • Lower risk of miscarriage

Disadvantages: Later diagnosis due to need for cell culturing

31
Q

What is foetoscopy?

A

Passing endoscope into amnion transabdominally under ultrasound guidance to visualise foetus

32
Q

What is cell-free foetal DNA (cffDNA)?

A
  • Fragmented foetal DNA present in maternal blood
  • Derived from placental trophoblasts
  • Detectable 4-5 weeks after gestation
33
Q

What techniques utilise cffDNA?

A
  • Non-invasive prenatal diagnosis (NIPD): Use of cffDNA to confirm diagnosis of disease (e.g. single gene disorders).
  • Non-invasive prenatal testing (NIPT): Use of cffDNA to test for possibility of disease followed by invasive technique to confirm diagnosis.
34
Q

When can cffDNA not be used for diagnosis?

A
  • Aneuploidy: Since in tact chromosomes are needed.
  • Single-gene defects: If mother is a carrier for disease being tested for, since the gene will be present in maternal blood.

Human Reproduction (21 decks)

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