screening of down syndrome in...
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![Page 1: Screening of Down syndrome in pregnancyukb.lf1.cuni.cz/ppt/Screening_of_Down_syndrome_2009_web.pdfPAPP -A • Glycoprotein, MW 750 000, elfo α2, maximum at the end of the 3 rd trimester,](https://reader034.vdocuments.us/reader034/viewer/2022042022/5e799810277e8e46547d5605/html5/thumbnails/1.jpg)
Screening of Screening of DownDown syndromesyndrome
in pregnancyin pregnancy
Marta KalousováInstitute of Clinical Chemistry and Laboratory
Diagnostics,
1st Faculty of Medicine and General University Hospital, Charles University, Prague
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Screening of Down syndrome Screening of Down syndrome
in pregnancyin pregnancy
• 1st trimester
• 2nd trimester
• integrated screening
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Recommendations of experts for Recommendations of experts for
screening of Down screening of Down syndomesyndome
-- laboratory requirementslaboratory requirements
• At least 1 000 screening examinations per year in a lab
• Lab specialist responsible for screening and its quality control
• Quality has to be checked at least twice a year
• The lab has guidelines for sample collection, transport and
storage which are in line with preanalytical phase
requirements
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• The lab co-operates with gynecologists and geneticians who are responsible for final evaluation of the screening results
• Results are provided by the lab within 3 days
• Results are given in absolute values as well as in multiples ofmedian for the gestational age
• Results are given to the requiring gynecologist who is responsible for further action
Recommendations of experts for Recommendations of experts for
screening of Down screening of Down syndomesyndome
-- laboratory requirementslaboratory requirements
![Page 5: Screening of Down syndrome in pregnancyukb.lf1.cuni.cz/ppt/Screening_of_Down_syndrome_2009_web.pdfPAPP -A • Glycoprotein, MW 750 000, elfo α2, maximum at the end of the 3 rd trimester,](https://reader034.vdocuments.us/reader034/viewer/2022042022/5e799810277e8e46547d5605/html5/thumbnails/5.jpg)
Screening of Down syndrome Screening of Down syndrome
in pregnancyin pregnancy
1st trimester
• Determination of PAPP-A - pregnancy-
associated plasma protein A
• Determination of free ββββ-hCG
• US of the fetus – nuchal translucence (NT),
presence of the nasal bone
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Screening of Down syndrome Screening of Down syndrome
in pregnancyin pregnancy
2nd trimester
• hCG
• AFP
• (unconjugated estriol) – triple test
• US of the fetus – in done earlier and
required for evaluation of the gestational
age
double test
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Integrated test (Wald 99)Integrated test (Wald 99)
1/ PAPP-A ( 9th – 11th week)
2/ NT ( 11th -13th week) phase I
3/ Second trimester (15th -18th week)
double or triple test phase II
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Integrated testIntegrated test
1st trimester
• PAPP-A
• US for determination
of gestational age
• NT
• Preliminary evaluation
by the medical doctor
2nd trimester
• AFP
• hCG
• Combined evaluation
with the results from
the 1st trimester
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Required dataRequired data
• Exact evaluation of gestational age -
US
• Age and body weight of the mother
• Date of blood collection
• Fetus – how many
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Markers Markers –– determination and determination and
evaluationevaluation
• Determination of absolute concetration in maternal serum
• Expression of the concentration in MoM (multiples of median), measured results has to be adjusted for body weight of the mother (dilution area) before calculation of MoM
• The same diagnostic kit has to be used – differences among various kits can be even 100 %!!!
• Influence of imprecise determination on the results of biochemical screening (immunochemical methods have intra-assay variability up to 10%, TRACE technology has variability 1-2%)
• The risk has to be evaluated by suitable software
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PAPPsPAPPs
pregnancypregnancy--associated plasma proteinsassociated plasma proteins
• detected immunochemically in plasma of pregnant
women
• 4 types
PAPP-A – Zn-binding metalloproteinase, role in
cleavage IGFBP and subsequent activation of IGF
PAPP-B – unknown function
PAPP-C = SP1 protein
PAPP-D = human placental lactogen (hPL)
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PAPPPAPP--AA
• Glycoprotein, MW 750 000, elfo α2, maximum at the end of the 3rd trimester, half-life after the birth 3-4 days
• Metalloproteinase, zinc-dependent (belongs to the metzincin superfamily of metalloproteinases), cleaves IGFBP-4, 2 and 5 (insulin like grown factor binding proteins), followed by release of IGF which play a role in regulation of local proliferative reactions – reproduction, wound heeling, atherosclerosis
• In pregnancy decreased in maternal serum in chromosomal anomalies (m.Down) in the 1st
trimester only!, at the end of pregnancy increased in preeclampsia, decreased in threatening abortion
• New marker of acute coronary syndrome
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PAPPPAPP--A during pregnancy and A during pregnancy and
after the birthafter the birth
months of pregnancy days after the birth4 10 3 127 6 9
PAPP-A
mU/l
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Concentration of Concentration of hCGhCG and AFP and AFP
during pregnancyduring pregnancy
week10 20 30 40
concentration
hCGAFP
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Human chorionic Human chorionic gonadotrophingonadotrophin
((hCGhCG))• Glycoprotein produced by synciciotrophoblast of placenta, necessary for function of the yellow body (production of progesteron)
• MW 36 700, αααα and ββββ subunit, α subunit the same as in LH, FSH and TSH. β subunit (145 AMK) similar in hCG and LH, 24 amino acid difference.
• Physiological occurence: pregnancy
• Pathological occurence: tumour from the chorionic tissue – trophoblastic disease (chorioCAa mola), germ cells testicular and ovarian tumours, rare other tumours.
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Human chorionic Human chorionic gonadotrophingonadotrophin
((hCGhCG))
β core
„free“β-hCG
β core – urinary excretion, very stable,
might be suitable for screening in the 2nd trimester
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Determined Determined hCGhCG• „Total“ hCG – mostly using polyclonal antibodies,
sufficient for dg of pregnancy
• ββββ-hCG – „specific“ hCG – required as tumour marker
• „free“ββββ-hCG - demanding preanalytical phase (disintegration of hCG mainly due to high temperature and false increase of „free“β-hCG )
• ββββ-core hCG – suitable for determination in the urine, but not at the end of the 1st trimester due to high levels of hCGand insufficient cleavage of hCG
• Hyperglycosylated („acidic“) hCG – characteristic for immature placenta at the beginning of pregnancy and for chorioCA. According to some studies present with higher probability in the urine of women with fetus with m.Down.
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hCGhCG
0.1 1 10 Log MoM
normal
Edwards Down
Risk of M.Down
MoM hCG>2,5
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αααααααα ––11--fetoprotein (AFP)fetoprotein (AFP)
• Glycoprotein, structurally similar to albumin
• Function: binds estrogens, transport of fatty acids, immunosuppressive effects
• Physiological production: yolk sack and fetalliver
• Pathological production: liver tumours, germ cells testicular and ovarian tumours, less frequently GIT and other tumours
in pregnancy increased in maternal serum in neural cord defects, omphalocele, spontaneusabortion
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AFPAFP
0.1 1 10 Log MoM
normal
Down
Edwards
Risk of M.Down
MoM AFP<0,5
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Evaluation of results of biochemical Evaluation of results of biochemical
screening of chromosomal anomalies in screening of chromosomal anomalies in
pregnancy pregnancy –– „„likelyhoodlikelyhood ratioratio““(Knight and Palomaki. J Clin Immunoassay 1990)
0.2 1 5
MS AFP MoM
the ratio of the lenghts of
the sections is evaluated
/→→→→ risk
Down normal
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Evaluation of Evaluation of atypicalityatypicality of results of of results of biochemical screening of chromosomal biochemical screening of chromosomal
anomalies in pregnancyanomalies in pregnancy(Wright et al. Ann Clin Biochem 1993)
0-0.3 0.3
0
-0.3
0.3
→ Log (MoM AFP).10-1
→Log (MoM
hCG).10-1
Edwards
NCD
Down
gemini
(trimini)
Down ?
Mahalanobis
distance –
from the centre
(normal)
healthy
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EstriolEstriol in blood during pregnancyin blood during pregnancy
• Increases during pregnancy
• Produced by placenta, conjugated in the liver, excreted into the urine
• determined uE3 – unconjugated estriol
• Chylosity interfers with the determination
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Problems in evaluation of the risk Problems in evaluation of the risk
of chromosomal anomaliesof chromosomal anomalies
• chorioCA and mola hydatidosa – high hCG and SP1, often various AFP – looks like m.Down or gemini
• Reduction of number of fetus in multiples pregnancies after IVF – often extremely high AFP and hCG, the concentrations change very quickly.
• Multiple pregnancies – elevation of biochemical markers is often non-symmetric, may look like NCD or m.Down
• Silent abortion or intrauterine fetus death – first elevation of biochemical markers, then decrease
• Donated ovulum – often from a younger donor – for evaluation of the risk – adjustment for body weight of the carrier, age adjustment for the biological mother
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Positive findingsPositive findings
• optimal FPR (false positivity rate) – for risk 1:300 and higher genetic consultation recommended
• Collection of chorionic villi (11th -13th week)
• Amniocentesis (16th -18th week, possible from the 12th week)
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Integrated testIntegrated test
30
40
50
60
70
80
90
100
0 2 4 6 8 10
Falešná pozitivita (%)
Dete
kce (%
)
Triple test
Double test
Integrovaný test
Integrovaný test - PAPP-A, NT, AFP, hCG
False positivity (%)
Intergrated test – PAPP-A, NT, AFP, hCG
Integrated test
Detection
(%)
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Possibilities of screening
90-93%65%75-80%effectivity
uE3
(unstable)
hCG
AFP
Nuchal tranlucence(NT)
free β hCG
(unstable)
PAPP-A
Integrated2nd trimestr1st trimestr
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LiteratureLiterature
• Zima T. : Laboratory diagnostics. 2nd Edition.
Galén Karolinum Praha 2007, 906 p. in Czech
• www.cskb.cz – recommendation for screening
• www1.lf1.cuni.cz/screeningDS