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Obstetrics > Genetic Screening > Flashcards

Genetic Screening Flashcards

1
Q

Components of the first trimester screen? Detection rate for Downs?

A

NT, PAPP-A, free or total HCG

82-87%

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2
Q

Most common aneuploidy in products of conception?

A

Trisomy 16 (non-viable)

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3
Q

Most frequent monosomy?

A

Turner’s (Monosomy X)

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4
Q

Most common autosmal aneuploidy in LIVE born infants?

A

Trisomy 21

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5
Q

When can you perform a NT?

A

10w0d - 13w6d

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6
Q

What is defined as an enlarged NT?

A

> /= 3.0 mm

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7
Q

With an enlarged NT what is the likelihood of fetal aneuploidy?

A

50%

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8
Q

What structures produce AFP?

A

Glycoprotein secreted by the yolk sac and liver of the fetus

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9
Q

What is the detection rate for open neural tube defects with an elevated maternal serum AFP

A

65-80%

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10
Q

Is msAFP elevated in CLOSED neural tube defects?

A

Nope!

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11
Q

At what gestation does the neural tube close?

A

4 weeks

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12
Q

What other conditions (besides open NTD) are associated with elevated AFP?

A
  • Multiple Gestation
  • Fetal abdominal wall defects
  • Fetal nephrosis
  • Fetal demise
  • Placenta conditions that increase risk of adverse outcomes later on in pregnancy
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13
Q

When can you perform cell free DNA testing?

A

9-10 weeks gestation (until term)

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14
Q

What factors affect the quantity of fetal fraction in cf DNA?

A 
Gestational Age
Maternal BMI
Med exposure
Maternal race
Aneuploidy status
Fetal or maternal mosaicism
Single or multiple gestation
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15
Q

Which screening test in the most sensitive and specific for the common fetal aneuploidies?

A

cfDNA

> 98-99%

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16
Q

What GA is CVS testing performed?

A

10w0d-14w0d

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17
Q

Risk of materno-fetal hemorrhage with CVS testing?

A

14%

18
Q

What GA is amniocentesis performed?

A

15w-20w

19
Q

Risk of materno-fetal hemorrhage with amnio?

A

2-6%

Give Rhogam!

< 12 wks = 50-120 mcg
> 12 wks = 300 mcg dose

20
Q

GA for First Trimester Screen + components

A

10-13w6d

NT, PAPP-A, B-Hcg

21
Q

GA for Quad Screen + components

A

15w-22w6d

AFP, BHcg, Estradiol, Inhibin A

22
Q

Describe integrated screening

A

“Integrated Screening”: NT + PAPP-A @ 10-13w THEN Quad Screen 15-22w

“Serum Integrated” - same, however no NT US

23
Q

What is the difference between between Stepwise Sequential and Contingent Screening?

A

In both first trimester screen is obtained

Stepwise Sequential: low risk does QUAD screen

Contingent: low risk does NO ADDITIONAL tesing

24
Q

Components of Stepwise Sequential Screening? GA?

A

First tri screen: NT, PAPP-A, Hcg (10w-13w6d)

Low risk: THEN QUAD (AFP, Bhcg, Estradiol, Inhibin A) 15-22w

High Risk: Diagnostic vs cfDNA

25
Q

Components of Contingent Screening? GA?

A

First Tri Screen: NT, PAPP-A, Hcg (10-13w6d)

Low Risk: No testing
Medium: QUAD (15-22w)
High: Diagnostic vs cfDNA

26
Q

Risk fo Downs Syndrome w/ maternal age > 40

A

1:51

27
Q

When a cystic hygroma is identified in the first trimester, what percentage of fetuses are aneuploid?

A

50%

28
Q

US Findings:

  • Thickened Nuchal Fold
  • Echogenic Cardiac foci
  • Echogenic bowel
  • Short humerus
  • Absent nasal bone
A

Down’s Syndrome

29
Q

In the second trimester- what is the most sensitive and specific finding for Down Syndrome?

A

Thickened nuchal fold

30
Q

Soft markers on US for Downs Syndrome in SECOND trimester?

A 
Echogenic Cardiac Foci
Pyelectasis
Echogenic bowel
Thickened nuchal fold
Mild ventriculomegaly
Choroid plexus cysts
Shortened femur length
31
Q

What anomalies are associated with an increased NT (> 3 mm)

A

Aneuploidy
Congenital heart defects
Abdominal wall defects
Diaphragmatic hernies

32
Q

What percentage of fetuses with increased NT measurement (> 3 mm) will have aneuploidy?

A

50%

33
Q

At what gestational age is NT measurement MOST sensitive in screening for aneuploidy?

A

13 weeks

34
Q

Quad Screen Results for Down Syndrome?

A

PAPP-A = low
B-hcg = high
Estradiol = low
Inhibin A= high

DOWN (low) unless they are HI (hcG, Inhibin A)

35
Q

Findings of “lemon sign” and “banana sign” on ultrasound are most consistent with which of the following congenital anomalies

A

Open neural tube defect

36
Q

Tell me about cell free fetal DNA testing

A

Noninvasive prenatal testing that using cell free fetal DNA from the plasma of the pregnant woman

Detection rate for Trisomy 13/18/21 is > 98% for each

Very low false positive rates < 0.5%

Most sensitive and specific screening test for common aneuploidies

**only screening test that can tell you gender and sex chromosome aneuploidies

37
Q

Amniocentesis vs CVS

A

CVS earlier (10-12 wks), can’t measure AFP, tissue specimen, inappropriate for diagnosis of NTD

Amniocentesis (after 15 wks), can measure AFP, samples individual cells, appropriate for NTD detection

38
Q

How is Fragile X syndrome inherited? Mutation on what gene?

A

X linked recessive
FMR1 gene
Tri-nucleotide CGG repeats

< 45 repeat unaffected
Intermediate 45 - 54 repeats
Pre-mutation 55-200 repeats
Full mutation > 200 repeats

39
Q

Occurrence risk of NTD?

A

*multi factorial (environmental and genetics)
*having family members with condition increases risk

General population 0.3% (400 mcg folate/day)
With one affected child 2-4% (4 g folate/day)
With two affected children 10%

Start 1-3 months prior to conception

40
Q

‘folate resistant’ NTD?

Folate will NOT prevent them, increased dose not necessary

A

Valproic acid in first trimester
High fetal glucose levels
First trimester fever or prolonged elevated maternal temperature (sauna use)
Obesity

41
Q

Is there anytime where an omphalocele would be considered “normal”

A

YES! Between 9-11 wks gestation (with herniation of the hind gut in normal development)

Obstetrics (26 decks)

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