Maternal Serum Screen

Question 1

What is a Screening Test?

-it is a ____ ________, and not a diagnostic test

-the result is a ________, and not a certainty
——-_________= higher likelihood/ risk of the disease
——-________=lower likelihood/ risk of the disease

The screening procedure itself does not diagnose the illness

Answer 1

risk assessment

likelihood

Positive
Negative

Question 2

____________

-Identification, from among apparently healthy individuals, of those sufficiently at risk of a specific disorder to justify a subsequent diagnostic test or procedure

-Screen with a less-invasive test: followed by a more invasive test to confirm diagnosis

Answer 2

Screening

Question 3

What is sensitivity and specificity?

Sensitivity and specificity are measures of a test’s ability to correctly classify a person as having a disease or not having a disease.

___________-is the ability to assign an individual with the disease as positive. A highly sensitive test means that there are few false _________ results, and thus fewer cases of disease are missed.

__________- is the ability to assign an individual who does not have the disease as negative. A highly specific test means that there are few false ________ results.

Answer 3

Sensitivity
Negative

Specifity
Positive

Question 4

Criteria for Screening (True or False)

-you don’t screen for diseases that are not severe or diseases of high incidence

Answer 4

True

Question 5

Criteria for Screening (True or False)

-disorder should be well-defined, with known prevalence

-severity of disease (high) vs. prevalence (low)

Answer 5

True

Question 6

Criteria for Screening (True or False)

-disorder should represent a substantial public health burden

Answer 6

True

Question 7

Criteria for Screening (True or False)

-there may not be an effective remedy for the disorder

Answer 7

True

Question 8

Criteria for Screening (True or False)

-tests should be simple, safe, stable

Answer 8

True

Question 9

Criteria for Screening (True or False)

-cost effective: cost of health care (high) vs. cost of screen (low)

Answer 9

True

Question 10

Criteria for Screening (True or False)

-Ethical: follow-up diagnostic procedures in place

Answer 10

True

Question 11

Criteria for Screening (True or False)

-made available to the most of population

Answer 11

True

Question 12

Criteria for Screening (True or False)

-distribution of test values in affected populations is known

Answer 12

True

Question 13

Criteria for Screening (True or False)

-degree of overlap with unaffected populations is small, and the cut-off (or decision point) is defined

Answer 13

True

Question 14

Criteria for Screening (True or False)

-follow up testing: risk of miscarriage, use of therapeutic abortion is an ethical issue, parent’s choice in Canada

Answer 14

True

Question 15

Limitations of Screening Tests (1 of 3)

1.Cut off values for populations of unaffected & affected overlap
—–screening “cut off” point used to determine negative and positive values refer to marker concentrations

2. False negative: below the cut-off there is a segment of the affected population who will be screen-negative.

3.False positive: above the cut-off there is a segment of the unaffected population who will be screen-positive

Question 16

Limitations of Screening Tests (2 of 3)

4. detection rate (Sensitivity)
   ——-the fraction of the affected population that is screen positive
5. false positive rate (Specificity)
   ——the fraction of the unaffected population that is screen positive

Note: No screening tests have a 100% detection rate; all screening tests have some false positives.
Ideally?
Sensitivity = detection rate = does the screen detect ALL those affected?

Specificity vs. false positive rate = does it detect ONLY those who are affected?

Question 17

Limitations of Screening Tests (3 of 3)

6. Can we change the screening cut-off?
   —–Increase cut off:
   decrease false positive rate, decrease detection rate

—–decrease cut off:
increase detection rate, increase false positive rate

Must have a huge amount of data before changing cut-off!

Question 18

__________ screening:

To determine the likelihood the baby may havetrisomy 21 (Down syndrome)ortrisomy 18.

Anyone may have a pregnancy with trisomy 21 or trisomy 18, regardless of their family history.

-This chance increases with the age of the mother or the age of egg donor.

-Prenatal screening poses little risk to the pregnancy as it involves ultrasound and blood work.

—–enhanced first trimester screening(eFTS)

—–maternal serum screening(MSS)

—–Non-invasive prenatal testing(NIPT)

Answer 18

Pre-natal

Question 19

__________ _________ Screen

-Testing the serum of the mother

-goal is to identify fetus at risk for a specific disorder

-blood test for certain biochemical markers is a good preliminary test

Answer 19

Maternal Serum

Question 20

_______ ________ _________(NSO)

-screens newborn blood spot samples for groups of diseases.

Answer 20

Newborn Screening Ontario

Question 21

Newborn Screening Ontario

__________ Diseases - where the body is unable to break down certain substances in foods, like fats, proteins or sugars

Answer 21

Metabolic

Question 22

Newborn Screening Ontario

__________ Diseases - where the body produces too much or too little of certain hormones

Answer 22

Endocrine

Question 23

Newborn Screening Ontario

________ _________ Disease (SCD) - which affects the movement of oxygen in the blood

Answer 23

Sickle Cell Disease

Question 24

Newborn Screening Ontario

_________ ________ - which causes problems with breathing and growth

Answer 24

Cystic Fibrosis

Question 25

Newborn Screening Ontario

________ __________ ________ _________(SCID) - which affects the body’s ability to fight infections

Answer 25

Severe Combined Immune Defficiency

Question 26

Newborn Screening Ontario

________ __________ _________ (SMA) - which causes muscle weakness and wasting

Answer 26

Spinal Muscular Atrophy

Question 27

Newborn Screening Ontario

______ _________ ________ ________ (CCHD) - which affects the quantity of oxygen in the blood.

Answer 27

Critical Congenital Heart Disease

Question 28

Newborn Screening Ontario (NSO)

Specimen: small blood sample if place on a paper slide. About 3-5 drops of baby’s blood is needed for all these tests

Tandem Mass Spectrometry (flow-injection):
—-Amino acidopathies (i.e. phenylalanine, tyrosine etc.)
—Organic acidopathies and fatty acid oxidation defects (i.e. C3, C8, C14:1, acylcarnitines etc.)

Tandem Mass Spectrometry (LC-MSMS):
—Congenital adrenal hyperplasia (2nd tier steroid profile)
—Organic acidopathies (2nd tier methylcitrate assay)

Immunoassay:
—Congenital adrenal hyperplasia (17OHP)
—Congenital hypothyroidism (TSH)
—Cystic Fibrosis (IRT)

Enzymatic assays:
—Biotinidase
—Galactosemia

HPLC:
—Hemoglobinopathies

DNA:
—Severe Combined Immunodeficiency

Question 29

_______ _________ _________ (NTDs)

-all or part of the neural tube fails to close completely during fetal development.

-defects of spinal cord & brain derived from a structure in the developing embryo called the neural tube

-Canadian incidence: 1/2000 births (does not vary with maternal age)

Answer 29

Neural Tube Defects

Question 30

Neural Tube Defects (NTDs)

open defect (most common)
_______ ______: failure of spinal cord to close
___________: failure of skull to close, and neural tissue left exposed

_______ defect
–defect covered with bone & skin
–less impairment

Answer 30

Spina bifida
Anencephaly

Closed

Question 31

________ ________

Pathophysiology:
–paralysis of lower limbs
–loss of motor control of bladder, bowels
–hydrocephalus (water on brain)
–mental disabilities (variable)

Answer 31

Spina Bifida

Question 32

Spina Bifida

______________:
the spinal cord is involved & protrudes from a hole in the bone of the spine

____________:
the spinal cord does not leave the protective bone tube (less severe)

Answer 32

Myelomeningocele

Meningocele

Question 33

___________
Complete or partial absence of the cranial vault, the forebrain, the midbrain, membranes & skin & possibly spinal cord
newborns with severe form die shortly after birth

Answer 33

Anancephaly

Question 34

NTDs cont’d

exact cause of NTDs is not clear:
-__________ component
—–family history, previous affected birth
—–likely a genetic mutation: folic acid may prevent a genetic mutation

-__________ component
—–higher frequency in Caucasians of Celtic Irish, Scots and Welsh descent

-_________ component
—–daily intake of folic acid one month before conception & during pregnancy has been shown to reduce the risk

Answer 34

genetic

ethnicity

dietary

Question 35

How do we detect NTDs?

-fetal proteins leak into amniotic fluid

-proteins enter maternal circulation by transfer & diffusion across placental membranes

-alpha-fetoprotein (AFP) detectable in both amniotic fluid & maternal serum

-open NTDs: levels of AFP are increased in both amniotic fluid & maternal serum

Question 36

_______ __________

-the first marker used for MSS

-protein: MW 70kDa, 591 aa

-synthesized initially by fetal yolk sac & later by fetal hepatocytes

-elevated amniotic fluid AFP concentration crosses the placenta, and leads to increased amounts in the maternal blood

-fetal blood levels peak 10-13 weeks gestation & then decline until term

-maternal serum levels peak at 28-32 weeks gestation, & then decline until term

Answer 36

Alpha-fetoprotein

Question 37

Analysis of Maternal Serum AFP (MSAFP)

Maternal blood at __-___ weeks gestation

Answer 37

16-20

Question 38

MSS Markers: Reporting & Interpretation

MSS Markers are reported in units called ____________ ___ ___ __________ (MoM)
-units correlate to the risk of NTDs
-units more reliable & allow for inter-laboratory variation / comparisons

-it is the maternal serum marker conc’n (ug/L) median reference for serum marker for gestational age
-increased AFP MoM levels above the cut-off indicate presence of NTD
-Correction factors used to account for maternal age, race, weight, gestational age, level of nutrition, diabetes

Answer 38

Multiples of the Median

Question 39

Interpretation of MSAFP Results

-MSAFP cut-off is ___ - ___ MoM
-levels above the cut-off is a _____ screen and require further investigation
-MSAFP detects most NTDs:
—-open spina bifida ___-___% of cases
—-anancephaly > ___% cases

-follow up testing more invasive, but more conclusive

Answer 39

2.0-2.5
positive
70-80
90

Question 40

Follow-up Testing for Screen Positive MSAFP

Question 41

_____________

-ultrasound used to guide needle
-collect ~20 mL
-risk: up to 0.5% (1:200) spontaneous miscarriage
-measure AFP, AchE

Answer 41

Amniocentesis

Question 42

________ _________ (_______ __)
-extra copy of long-arm of chromosome 21

-mental retardation, low muscle tone, congenital heart defects, flat facial profile, larger protruding tongue

-incidence increases with maternal age: 1:1300 age 25, 1:365 age 35, 1:100 age 40, 1:30 age 45

-maternal age alone is a screening test

-most common serious disorder resulting from a chromosomal abnormality in live born babies

-A correlation between decreased MSAFP levels & DS first identified in 1984

-decreased maternal serum AFP levels
< 0.5 MoM are suggestive of DS

Problem: too much overlap

Answer 42

Down syndrome (Trisomy 21)

Question 43

Down Syndrome (Trisomy 21)

Confirmation test: ________ chromosome Cytogenetics analysis
—–amniocentesis (___-___ wks)
—–chorionic villus sampling (CVS) (__-___ wks)
—–percutaneous umbilical cord blood sampling (PUBS) (__-___ wks): high risk

_____- contains fetal cells from chorion that is placental tissue derived from fetal side of placenta
______-needle guided by Ultrasound through abdomen & uterine wall to umbilical cord: small sample of fetal blood obtained for testing

Answer 43

Karyotyping
15-20 weeks
10-13 weeks
18-20 weeks

CVS
PUBS

Question 44

________ ________ Screen
-3 markers in maternal serum measured by immunoassay during 2nd trimester: AFP, hCG, uE3

-Screens for NTDs and Down Syndrome
-test offered to all pregnant women in Ontario regardless of their age
-one blood sample taken at 16-18 wks

An ________ levels of hCG and ________ levels of unconjugated estriol (uE3) associated with Down Syndrome

Answer 44

Triple Marker

increased; decreased

Question 45

______ __________ ______________

-maternal serum marker for detection of fetus with Down syndrome, but not NTD

-hCG MoM of 2.5 or higher associated with DS

-only detects 40% of DS pregnancies if used alone (poor sensitivity if used alone)

Answer 45

Human Chorionic Gonadotropin

Question 46

________ ________

-early in second trimester, fetus begins to synthesize large amounts
——a complex series of enzymatic reactions involving fetal liver, fetal adrenal glands, & placenta
—-rises progressively throughout gestation
—-A decreased level in maternal serum is a predictor of DS & NTD

Answer 46

Unconjugated Estriol

Question 47

Interpretation: Triple Marker Screen

suspected NTDs
1. refer to Genetics
2. Level II ultrasound
3. amniocentesis: analyze amniotic fluid AFP & acetylcholinesterase

suspected DS
1.refer to Genetics
2.Ultrasound
3.confirm with karyotyping (amniocentesis, CVS, PUBS, )

Answer 47

Question 48

Laboratory Considerations

Question 49

Calculating Risk & Reporting

A “screen positive” result means fetus has an increased chance of having one of the screened conditions
Confirmation testing may conclude that baby does not have one of the conditions (i.e., false positive rate or specificity of the screen)

A “screen negative” result means chance for having a baby with the condition screened for is lower than the standard screening cut-off and is not considered to be at an increased risk
does not guarantee birth of a baby without problem
for every pregnancy, there is a 2-3% chance for having a baby with some problems at birth

Question 50

Quad Screen- Dimeric Inhibin A (DIA)
-Ontario’s screening programs have added 4th serum marker:

-_________- are glycoprotein hormones secreted by ovaries in non-pregnant women, and by the placenta
-In a non-pregnant state, it suppresses the secretion of FSH
——–function in pregnancy is unknown

-levels ________ in both NTD and DS
——–measurement of additional markers has been shown to increase detection rate & decrease false positive rates

Answer 50

inhibin

increased

Question 51

_______ _________ _________

Performed at 11-14 wks gestation (earlier than triple screen), measurement of 2 serum markers AND Ultrasound:

1. free-beta subunit hCG (in serum: is not protein bound)
   ———–__________ in DS
2. pregnancy associated plasma protein A (PAPP-A)
   ———-___________ in DS
3. includes a fetal ultrasound: nuchal translucency (NT)
   ————NT __________ with DS and some other birth defects

Answer 51

First Trimester Screening

1.increased
2. decreased
3. increased

Question 52

_________ ____________

-measure fluid accumulation at the back of the fetal neck (nuchal region between back of spine and skin)
-measurements greater than 3.0 mm need further investigation (usually no greater than 1 or 2 mm thick)

Answer 52

Nuchal Translucency

Question 53

First Trimester Screening

Question 54

More Recent Screening

Question 55

Trisomy 18

Question 56

cell free- DNA

Question 57

Review Questions

Answer 57