Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Path 19.05 > 20.05.08 Maternal Serum Screening and Down Syndrome screening methods > Flashcards

20.05.08 Maternal Serum Screening and Down Syndrome screening methods Flashcards

1
Q

What is the UK national Screening committee’s definition of screening

A
  • The process of identifying apparently healthy people who may be at increased risk of a disease or condition.
  • They can then be offered information, further tests and appropriate treatment to reduce their risk and/or any complications from the disease or condition.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the NHS Fetal Anomaly Screening Programme (FASP)

A

-Offered to all pregnant women, to assess risk of Trisomy 21 and a number of fetal anomalies.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How was Downs syndrome risk originally based

A
  • Advanced maternal age used to identify increased risk of Downs syndrome in pregnancy.
  • However, detection rate was only 30%, with 5% false positive rate.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What method is now used to identify women with increased risk of Down syndrome

A

Maternal serum screening, ultrasound and maternal age

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What should all women be offered regarding Downs syndrome screening

A
  • Information to help them decide if they want screening or not
  • A down syndrome screening test that meets national standards
  • An ultrasound scan to check for physical abnormalities in fetus.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the Down syndrome screening pathway

A
  • Undertaken from 10 to 20 weeks of pregnancy
  • Couples receive counselling about procedure, possible outcomes and decisions they may face.
  • Screening is nuchal translucency measurement, maternal serum testing or both.
  • Screen positive if greater to or equal 1:150
  • If risk is above this then offered invasive testing (AF or CVS).
  • 3 day TAT
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is prevalence

A

Number of individuals in a population with the target condition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is sensitivity

A

A screens ability to positively identify individuals who have the target condition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is specificity

A

A screens ability to not detect individuals who do not have the target condition.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the detection rate

A

Proportion of affected individuals with a positive screening result

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a screen positive rate (SPR)

A

Proportion of individuals who will be given a high risk result following screening.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is a false positive rate (FPR)

A

Proportion of unaffected individuals with a positive screening result. Complement to specificity. i.e Specificity= 100-FPR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is a false negative rate (FNR)

A

Proportion of women who are given a lower risk result but have an affected pregnancy. Complement to sensitivity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is nuchal translucency

A
  • Maximum thickness of the subcutaneous translucency between the fetal skin and soft tissue overlying the cervical spine.
  • Measured between 11 and 14 weeks.
  • Combined with maternal age and size of baby to calculate risk.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What NT is associated with aneuploidy

A
  • NT ≥3.5mm
  • Highest to lowest prevalence= 21, 18, 13, 45,X and triploidy.
  • Also linked to structural malformations or genetic syndromes.
  • Diagnostic test offered
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What percentage of pregnancies have NT ≥3.5mm

A

1%

17
Q

What is maternal serum screening

A

Measuring the levels of serum analytes that have passed from fetus to mother’s blood
-Multiples of Median (MoM) are calculated for each serum marker
-

18
Q

How is risk determined using maternal serum screening

A
  • Multiples of Median (MoM) (serum marker concentration for a pregnant woman) is divided by the median concentration value for unaffected pregnancies of the same gestational age.
  • Mother’s serum results, age, weight and gestation all used in risk calculation
19
Q

Why is the median marker level used (rather than mean) for serum results

A

-Median is not skewed by very high or very low values.

20
Q

What screening strategy is recommended

A
  • Combined screening
  • serum screening (β-hCG, PAPP-A) and NT
  • Can be done at 10-14 weeks
  • If screen positive result received, a woman should have rapid access to appropriate counselling.
  • Looks for trisomy 13, 18 and 21
21
Q

What factors affect serum screening

A
  • Serum marker levels tend to be decreased in heavier women and increased in lighter women.
  • Serum marker levels tend to be higher in Afro-Caribbean women than Caucasian.
  • IVF can alter levels (β-hCG and hCG levels higher in IVF pregnancies).
  • AFP and uE3 levels tend to be lower in women with insulin dependent diabetes mellitus
  • Smokers have lower PAPP-A, free β-hCG and hCG levels
22
Q

What kind of screening is recommended for twin pregnancies

A
  • Quadruple screening
  • AFP, β-hCG, uE3+ Inhibin A
  • Done at 14-20 weeks
23
Q

What risks are there for screening twin pregnancies

A
  • Marker levels raised in twin pregnancies
  • One twin could be affected and the other not
  • Dichorionic twins and monochorionic twins have different serum levels
  • Procedural risk for prenatal testing is higher for twins.
24
Q

What else is the quadruple test used for

A
  • Downs syndrome testing

- When NT is not available, not as accurate as combined.

25
Q

What is the fetal anomaly scan

A
  • Performed at 18-20 weeks
  • Detailed ultrasound scan to detect foetal anomalies.
  • Includes heart defects, cleft lip/palate, cystic hygroma, neural tube defects, polydactyly, talipes, short femur
26
Q

What is the policy for reporting normal Down screening results

A
  • Should not be referred for further assessment of chromosome abnormalities even if certain findings are seen at 18-20 fetal anomaly scan.
  • Exception is if nuchal fold >6mm, echogenic bowel, small measurements (below 5th centile), ventriculomegaly
27
Q

Prenatal testing following high risk screen result: CVS

A
  • 1-2% procedural loss.
  • Same genetic origin as fetus but differentiated from it by 5-6 weeks gestation
  • Risk of CPM
  • Performed from 10-12 weeks
28
Q

Prenatal testing following high risk screen result: Amniotic fluid sampling

A
  • Performed at 16 weeks gestation.
  • Contains cells from fetal skin, urinary and respiratory tracts
  • 0.5-1% procedural loss
29
Q

Prenatal testing following high risk screen result: Fetal blood sampling

A
  • Sample of blood taken from umbilical cord at 18+ weeks
  • 2-2.5% procedural loss
  • Usually only done if previous prenatal test failed or showed findings of mosaicism.
30
Q

What is non-invasive prenatal testing

A

Isolation and testing of free fetal DNA (largely derived from placenta) circulating in mother’s blood. Levels are sufficient from 10 weeks gestation

31
Q

What is the basis of cffDNA aneuploidy testing

A
  • Looking for an over representation of DNA sequences from chromosomes 21, 18, 13.
  • Not reliable enough to be a diagnostic test but very sensitive and specific as a screening test for trisomy 21. Not as reliable for trisomy 18 and 13.
32
Q

What should happen for positive NIPT results

A

-Confirmed using an invasive diagnostic test such as CVS or amniocentesis.

33
Q

When is NIPT testing offered

A

Women with a risk of greater than 1:150

34
Q

Benefits of offering NIPT testing

A

-Reduces the need for invasive testing, thus reducing the number of miscarriages.

35
Q

What could be used in the future for screening programmes

A
  • Proteomics. To identify and characterise proteins in maternal serum from patients at high risk for trisomy 21, 18, 13.
  • SELDI-TOF MS, SDS-PAGE, MALDI-TOF
36
Q

What is serum marker PAPP-A

A
  • Pregnancy associated plasma protein-A
  • Levels optimum at 11 weeks.
  • Decreased in trisomy 21, 18, 13 and sex chromosome abnormalities.
37
Q

What is serum marker free β-hCG

A
  • Free β human Chorionic gonadotrophin (β hCG)
  • Effective in 1st and 2 trimester
  • Increased in DS, decreased in +13, +18
38
Q

What is serum marker AFP

A
  • Alpha fetoprotein (AFP)
  • 2nd trimester. Decreased in DS and fetal demise. Increased in some fetal abnormalities (neural tube defects, renal abnormalities)
39
Q

What is serum marker uE3

A
  • Unconjugated oestriol (uE3)
  • 2nd trimester
  • Decreased in +21, +13 and +18

Path 19.05 (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions