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HR MVST 1b > Prenatal Diagnosis > Flashcards

Prenatal Diagnosis Flashcards

1
Q

What percentage of neonates have a significant congenital abnormality?

A

2-3%

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2
Q

When do you carry out prenatal diagnosis tests?

A

High risk i.e. family history of genetic disease, maternal illness (DM), previous history of an abnormal pregnancy
Or abnormal screening test

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3
Q

What is screened for in a low risk pregnancy?

A

Major:
Congenital anomalies e.g. neural tube defects, congenital heart disease, brain malformations
Chromosome abnormalities

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4
Q

What are the common neural tube defects?

A

Anencephaly and spina bifida (90%)
Open defects –> neural tissue and meninges exposed
Closed = 15-20%

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5
Q

What is the test for neural tube defects?

A

Open: increased maternal serum alpha-fetoprotein
Closed: undetectable

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6
Q

Why has there been a decline in neural tube defects?

A

Better nutrition and dietary folic acid

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7
Q

What are the different types of chromosomal abnormality?

A 
Aneuploidy = addition or loss of whole chromosome
Addition or loss of part of a chromosome
Chromosome rearrangement (translocation or inversion)
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8
Q

How do you detect chromosome aneuploidies?

A

Cytogenetic analysis

Microarray analysis for addition or loss of part of a chromosome

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9
Q

What are the common trisomies?

A 
13, 18, 21, X
13 = Patau
18 = Edwards
21 = Down
XXY = Klinefelter
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10
Q

What is Trisomy 21? Describe the symptoms

A

Down Syndrome
Intellectual disability - mild to moderate
Dysmorphic - nasal flat bridge, up slanting palpebral fissures, epicanthic folds (fold of skin on medial upper eyelid), single palmar crease, protruding tongue, clinodactyly (curvature of 5th finger towards adjacent 4th finger)
Cardiac defects - 40% of cases

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11
Q

What is the incidence change of trisomy 21 with maternal age?

A

1:700 to 1:50 at maternal age 43

60% sponataneously abort

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12
Q

What is Trisomy 18? Describe the symptoms.

A 
Edward's syndrome
Severe learning disability
Dysmorphic - micrognathia, prominent occiput
Clenched overlapping fingers
Prominent heels and rocker-bottom feet
Cardiac defects
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13
Q

What is the incidence change of trisomy 18 with maternal age?

A

1:3000 to 1:500 at age 43

30% die within 1 month, 90% one year

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14
Q

What is Trisomy 13? Describe the symptoms

A

Patau Syndrome
Severe mental disability
Dysmorphic - cleft lip, cleft palate, holoprosencephaly, postaxial polydactyly, renal abnormalities, cardiac defects

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15
Q

What is the prevalence change of trisomy 13 with maternal age?

A

1:5000 to 1:1100 at 43

45% die within 1 month, 85% within 1 year

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16
Q

What is Turner Syndrome? What is the incidence?

A

1/5000

XO

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17
Q

What is Klinefelter Syndrome? What is the incidence?

A

1/1000

XXY

18
Q

Describe the progression of prenatal ultrasound scanning?

A

Booking scan 1 trimester less than 15w
Foetal anomaly scan 18-20w second trimester. Most abnormalities pciked up here
Fetal MRI for brain imaging

19
Q

What is the early pregnancy scan for?

A
  1. Establish gestational age accurately (essential for trisomy 21 screening)
  2. Fetal crown-rump length <12 weeks or
  3. Biparietal diameter >12 weeks.
  4. Nuchal translucency measurements. Between 11-13w gestatation. Non-specific
    V few abnormalities picked up here
    Test of viability, foetal number and in multiple pregnancies the chorionicity/amnionicity
    Detection of gross fetal abnormalities.
20
Q

Which conditions is increased nuchal translucency thickness seen with?

A

Trisomy 21
Cardiac failure associated with congenital heart disease
Venous congestion in head and neck caused by constriction of foetal body (amniotic band, superior mediastinal compression caused by diaphragmatic hernia, narrow chest in skeletal dysplasia)
Abnormal development of the lymphatic system
Impaired fetal movement due to neuromuscular disorder
Foetal anaemia/hypoproteinaemia
Congenital infection through anemia or cardiac dysfunction
Some rare single gene disorders

21
Q

What is the normal nuchal thickness?

A

2.5mm

>5.5 = 80% risk adverse outcome (abnormality/fetal or postnatal death)

22
Q

From when are neural tube defects detectable by antenatal ultrasound? What are the signs?

A

Anencephaly 10-14 weeks
Spina bifida 16-22 weeks
Indirect cranial or cerebellar markers are Lemon + Banana signs - tonsils of the cerebellum come down onto spinal canal
Most detected by 20 week anomaly scan

23
Q

What is Meckel-Gruber syndrome?

A

Example of an abnormality that leads to specific diagnosis
Encephalocoele
6 digits
Single gene disorder

24
Q

What are the modes of screening?

A

Maternal age
Serum screening
Combined screening using information from ultrasound and maternal serum tests

25
Q

Describe alphafetoprotein

A

Reaches maternal serum directly across placenta or indirectly from amniotic fluid across chorion and amnion and then uptake by maternal vasculature in the decidua.
Measure by immunoassay
Levels change with gestation (lower trimester 2 than 1)
Used to screen for NTDs and trisomy 21.
Need accurate estimate of gestation at which sample is obtained to interpret
Made by yolk sac and fetal liver

26
Q

What is the false positive problem in AFP serum tests?

A

Unaffected and spina bifida overlaps

At 5% false + rate around 75% open spina bifida cases detected. Balance between specificity and sensitivity.

27
Q

Why can you not use maternal age alone to screen for trisomy?

A

Because although risk rises, the majority of cases still occur in younger women

28
Q

What are the prenatal markers for Down Syndrome?

A

Maternal age
Nuchal scan
Brackets = multiple of median
Serum screening for AFP (0.75), unconjugated estriol (0.73), hCG (2/05)
If greater than 1 in 250 threshold risk, i.e. 5% false positive rate, give women amniocentesis

29
Q

Give examples of tests used in high risk pregnancies

A 
Invasive
CVS chorionic villus sampling
Amniocentesis
Fetal blood sampling
Non-invasive
Ultrasound
Free fetal DNA
30
Q

Describe CVS

A

Chorionic villus sampling
Enables samples to be taken in first trimester after 11 weeks
Fetally derived cells (trophoblast)
Maternal material must be discarded
Gives good preparations of DNA without culture
Chromosome analysis can be done rapidly within 24h, but best quality analysis after 2 weeks culture.
1-2% miscarriage risk.
Possible of surgical termination in 1 trimester.
Problem: testing placenta not fetus - some abnormalities are seen in the placenta but not the fetus so diagnositclaly difficult

31
Q

Describe amniocentesis

A

10-20 mls of amniotic fluid sampled transabdominally under US
16w gestation or later
Cells from amnion, fetal skin and urinary tract pelleted
Culture 2 weeks
Longer culture may be needed for DNA or biochemical studies - nb rapid trisomy screen results by PCR bypass this time requirement
0.5% risk miscarriage
Medical/late termination of pregnancy.

32
Q

What are the pros and cons of CVS?

A 
Pro
Earlier Diagnosis
Cons
Higher risk miscarriage
Extraembronic tissue
Possibility of confined placental mosaicism
33
Q

What are the pros and cons of amniocentesis?

A 
Pros
Fetal material
Lower risk miscarriage
Cons
Later diagnosis
34
Q

How do you investigate fetal structural anomaly?

A

Karyotype - misses inversions and translocations
Chromosomal microarrays +5%
DNA sequencing + ??%

35
Q

What is a foetoscopy and what is it used for

A

Foetal skin biopsy

Used for hereditary skin disorders e.g. epidermolysis bullosa

36
Q

What is cordocentesis and what is it used for?

A

Foetal blood sampling for chromosomal disorders, haematological disorders and congenital infection

37
Q

What is the total schema of Pre-implantanation genetic diagnosis?

A
  1. Genetically examine couple
  2. Genetic conclusion
  3. Fertilisation IVF or ICSI
  4. Blastomer biopsy
  5. PCR FISH
  6. Embryo transfer (not more than 2)
38
Q

What are the pros and cons of cell free foetal DNA?

A

No increased risk miscarriage
Easier sample collection
Earlier diagnoses (from 7 weeks)

39
Q

Describe cell free fetal DNA testing cffDNA

A

Originates from placenta
Represents whole fetal genome
Detectable from 4 weeks
% increases with gestation
10-20% total cfDNA
Cleared from circulation within 30 mins delivery
Shorter than maternal cfDNA 166bp cw 143 bp

40
Q

What is NIPD NIPT NIPS?

A

Non invasive prenatal diagnosis/testing/screening
NIPD for high risk cases - doesn’t require invasive test for confirmation ie single gene disorders, sex determination
NIPT NIPS for low risk cases. Aneuploidy. Requires invasive testing for confirmation.

41
Q

Give examples of use of NIPD

A

Fetal sex determination genes on Y chromosome - don’t need to test female.

HR MVST 1b (6 decks)

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