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MD1 - Reproduction Block > 7. Prenatal Screening > Flashcards

7. Prenatal Screening Flashcards

1
Q

How many babies are born/year

A

70,000

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2
Q

What percentage of babies have birth defects

A

4%

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3
Q

What kind of birth defects exist?

A

Structural Functional Genetic Chromosomal Biochemical

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4
Q

What is the most common chromosomal abnormality?

A

Trisomy 21 (1 in 600 ~ 1 in 1000) 2nd most common XXY (Klinefelter syndrome)

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5
Q

What information is important from taking a family history?

A
  • Should ask a 3 generation family history Including age of diagnosis
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6
Q

What questions should you ask when taking family history?

A
  • Inherited conditions - Down syndrome and other chromosomal conditions - Other birth defects, e.g. spina bifida, cleft/lip palate, cardiac defects, intellectual disability - Recurrent miscarriage - Unexplained perinatal deaths - Consanguinity - Ethnic background - IVF/Donor gametes
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7
Q

What is the risk of giving birth to a child with Down Syndrome?

A

Increases exponentially from 1 in 1411 at age 20-24 to 1 in 32 at age 45

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8
Q

What is the prevalence of neural tube defect?

A

1 in 500 o Spina bifida o Anencephaly o Encephalocele - Folate Should be taken before and during pregnancy

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9
Q

What are the benefits of prenatal testing?

A
  • Offers reproductive choice - Risk information - Choice of termination - Prepare psychologically - Help plan delivery and management - Provide reassurance
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10
Q

What are the 2 major types of prenatal testing?

A

Screening test - Offered to all pregnant women - Non-invasive - Taken by up to 80% pregnant women Diagnostic tests - Offered to women who are at increased risk of having a child with a birth defect - Invasive

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11
Q

What is the 1st trimester combined screening?

A
  • Blood taken at 10 weeks o 2 biochemical analytes measured - Ultrasound performed at 11 -13 weeks. o Nuchal translucency measured (oedema that occurs behind fetal neck) o Crown rump length (dating) - Other factos including maternal age Results/Cutoff - T21: 1 in 300 - T18: 1 in 175 Detection rate for T21 is 93% - 4.6% false positive result
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12
Q

What is the 2nd trimester combined screening?

A
  • Blood taken at 14-20 weeks (15-17 ideal) o 4 biochemical analytes measured - Maternal age Cutoff - T21 1 in 250 - T18 1 in 200 - Neural tube defects >2.0MoM Detection rate for T21 is 85%, with 6.5 false positive rate Detection rate for neural tube is 93% but ultrasound is recommended
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13
Q

What is NIPT/S?

A

(non-invasive prenatal testing/screening) – using Cell-free fetal DNA/RNA in maternal blood - Non invasive - ~10 weeks gestation - Uses new sequencing technology

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14
Q

What does Chronic cillus sampling (CVS) involve?

A
  • From 11 weeks gestation - Placental tissue - Ultrasound - Invasive 1% miscarriage - If termination of pregnancy requested, dilation & curettage under general anaesthetic (
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15
Q

What is Amniocentesis?

A

15-16 weeks gestation

Amniotic fluid (20ml) containing sloughed off fetal cells removed

Ultrasound

0.5% miscarriage

If TOP requested, by prostaglandin (>16 wks)

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16
Q

What is fish?

A
  • Fluorescence in site hybridization
  • Using probes on interphase cells to look for abnormalities in chromosome numbers
17
Q

What recessive conditions often present without a Fx?

A
  • Haemoglobinopathies (1 in 20 – ethnicity)
  • Ashkenazi jewish panel (7 conditions, 1 in 25 to 1 in 100)
  • CF (1 in 25 – Northern Europe)
  • Spinal muscular atrophy (1 in 40)
  • Fragile X syndrome (1 in 200)
18
Q

What is Robertsonian translocation?

A

Rearrangement on Acrosomic Chromosomes

19
Q

What re acrocentric chsomosomes?

A

Chromosomes with a small P arm

Examples (13, 14, 15, 21, 22)

20
Q

Balanced vs unbalanced translocation in Trisomy 21

A
  • Most common is 14;21
  • If they are balanced, has not loss any genetic material it will not cause any problems for the individual but may cause problems for offspring when inherited
  • Balanced translocation = carrier status and that will have no implication to individual unless genetic information has been lost
    But it can occur in the offspring
  • Unbalanced translocation between chromosome 14 and 21 leads to trisomy 21 = Down Syndrome
21
Q

How does unbalanced translocation cause Down Syndrome?

A
22
Q

Microarrays (DNA chips)

A
  • DNA sequences and/or gene expression
  • Can look at SNPs
  • Can look at larger changes – number of chromosomes and copy number variations
23
Q

What are chromosomal microarrays?

A
  • Array CGH (comparative genome hybridization) and SNP arrays
    o Also called molecular karyotyping
  • Probes (25 base oligonucleotides along entire genome)
  • Variable resolution
  • For deletions and microdeletions
24
Q

When should prenatal molecular karyotyping be performed?

A
  • a fetal abmormality identified on ultrasound scan
  • Nuchal translucency is >3.5mm
  • A banded (classical cytogenic) karyotype identifies a complex change
  • A family member has a microdeleton syndrome and a pregnancy is at risk
25
Q

What dooes the result of molecular karyotyping show?

A
  • Normal result does not exclude genomic abnormality
  • Presence of small deletion/duplication does not mean pathogenic
  • Some region of homozygosity may suggest autosomal recessive condition and/or consanguinity
  • Incidental findings
26
Q

What is pre-implantation genetic diagnosis?

A
  • Require IVF
  • One or two cell from 3 day old dividing zygote
    Can do DNA testing, FISH, now chromosomal microarrays
27
Q

What are the analytes in the second trimester maternal serum screening test? and what indicates an increased risk of Trisomy 21

A
  • a-fetoprotein (Reduced)
  • Oestriol (Reduced)
  • hCG (Increased)
  • Inhibin A (Increased)
28
Q

What are the analytes taken in the first trimester?

A
  • hCG
  • PAPP-A

If both are reduced = Increased Risk of Tri18

If hCG is increased and PAPP-A is reduced = Increased risk for Trisomy 21

MD1 - Reproduction Block (15 decks)

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