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Fetus > Prenatal diagnosis > Flashcards

Prenatal diagnosis Flashcards

1
Q

What are the benefits of prenatal screening

A

Parental reassurance of normal
If abnormality is detected the increased options eg. further testing, referral, counselling.
Altered obstetric management
Facilitated neonatal management

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2
Q

What are the risks of prenatal screening

A

Parental anxiety
False positives
Pregnancy complications
Pregnancy loss

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3
Q

What are the current methods for screening for chromosomal abnormalities

A

Integrated prenatal screening
First trimester combined screeening
Quadruple maternal serum screening

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4
Q

What is integrated prenatal screening

A 
Nuchal translucency
PAPP-A
hCg
AFP (alpha fetoprotein)
uE3
inhibin A
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5
Q

What is first trimester combined screening

A

Nuchal translucence, hCG, PAPP-A

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6
Q

What is quadruple maternal serum screening

A

hCG, AFP, uE3, inhibin A

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7
Q

What is nuchal translucency

A

Fluid-filled space between back of fetal neck and skin
Measured between 11-13 +6/7
Increases with gestational age
>3-3.5mm cosidered elevated

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8
Q

What happens if nuchal translucency is elevated

A

Diagnostic testing
Fetal echocardiogram around 20 weeks
Detailed anatomy scan 18-20 weeks
Genetic counselling

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9
Q

What is elevated nuchal translucency indicative of

A

Trisomies 21, 18, 13, Turner syndrome
spontaneous fetal loss
Cardiac defects, diaphragmatic hernia, pulmonary defects, skeletal dysplasia, congenital infection
Chance on normal birth decreases with increased size

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10
Q

What are the non-invasive methods of chromosomal evaluation

A

Fetal cells from maternal blood

Preimplantation embryos

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11
Q

What are the invasive methods of chromosomal evaluation

A

Amniocentesis
Chorionic villus sample
Fetal blood

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12
Q

What can testing evaluate

A

Chromosomal aberrations- trisomy, monosomy, polyploidy, marker chromosome, deletion, duplication, inversion, translocation
Genetic aberrations
Infectious disease
Biochemical markers

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13
Q

What is amniocentesis

A 
Sample of amniotic fluid
Percutaneous
20g needle
20cc amniotic fluid
Results in 2-3 weeks
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14
Q

What are the complications of amniocentesis

A 
1% pregnancy loss
Increased risk if needle larger than 18g, multiple needle insertion, discoloration of fluid, high AFP, multiple late miscarriages, previous vaginal bleeding, placental perforation
Leakage of amniotic fluid
amnionitis
Vaginal bleeding
Needle puncture of fetus
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15
Q

What are the potential long term complications of amniocentesis

A

Respiratory distress

Isoimmunisation

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16
Q

How is HIV related to amniocentesis

A

Increased rates of vertical transmission

Chemoprophylaxis before amniocentesis can prevent

17
Q

What is chorionic villus sampling

A

Direct analysis- trophoblast cells of placenta. Results in hours but vulnerable to mitotic error
Cultured analysis- fibroblast like cells of villus stroma. results in 10-14 days, more accurate

18
Q

What is true chromosomal mosaicism

A

2 or more abnormal cell lines detected in 2 or more cultures from the same individual

19
Q

What is pseudomosaicism

A

2 abnormal cell lines found in only 1 culture

20
Q

What is the detection rate of mosaicism

A

1-2% in CVS

0.1% in amniocentesis

21
Q

What is the clinical outcome of mosaicism

A

Strongly dependent of specific chromosome involved + number of trisomic cells in placenta + fetus

22
Q

What are the 4 possible conditions if trisomy mosaicism is detected in CVS

A
  1. Mosaicism only in placenta, not affecting fetus or placental function
  2. Mosaicism only in placenta, affecting placental function (IUGR) but not fetus
  3. Trisomic cells in both placenta and fetus
  4. Trisomic cells in placenta, uniparental disomy in fetus
23
Q

What happens if mosaicism is detected at amniocentesis

A

Trisomic cells are probably present in fetus but true level and distribution cannot be accurately assessed with any prenatal procedure so ultrasound used

24
Q

What is uniparental disomy

A

Individual inherits 2 copies of a chromosome pair from one parent and no copy from the other parent

25
Q

What are the mechanisms of UPD

A

Trisomic rescue- loss of chromosome from trisomic zygote
Monosomic rescue- duplication of chromosome from monosomic zygote
Gamete complementation- fertilisation of gamete with 2 copies of same chromosome by gamete with no copies

26
Q

What are the clinical consequences of UPD

A

Parental imprinting
Unmasking of recessive conditions
Molecular UPD testing should be considered for particular chromosomes with known phenotypic effects- 6, 7, 11, 14, 15

27
Q

What factors should be considered when predicting outcome of mosaicism

A 
The chromosome involved
Tissues affected and level of trisomy in those tissues
Method of ascertainment
Ultrasound findings
Presence of UPD
Previous case reports
28
Q

Who can be offered non invasive prenatal testing

A 
Maternal age related risk
Positive results on maternal serum screening
Abnormal ultrasound findings
Prior pregnancy with aneuploidy
Parental robertsonian translocation
29
Q

What are the aims of NIPT

A

Reduce exposure of fetus to risk
Reduce false positives
Enable high detection rate
Easily offered to all pregnant women

30
Q

What are the sources of fetal DNA

A

Fetal cells- 1/billion of total cell population, requires mechanical/biochemical isolation
Cell free DNA- maternal and fetal cfDNA in maternal blood. 2-20% fetal

31
Q

What is fetal cfDNA

A

Small DNA fragments 150-200bp released through apoptosis

Detectable from 7 weeks

32
Q

What are the methods of analysing cfDNA

A

Direct analysis

Massive parallel sequencing

33
Q

What are the advantages of NIPT

A

Reduces unnecessary procedures in borderline high risk women

More equivocal risk assessment

34
Q

What are the disadvantages of NIPT

A

Not available on NHS
Expensive
Still classified as screening not diagnosis
Results take 7-10 days

Fetus (18 decks)

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