Transcript Down`s syndrome screening

Pregnancy & Newborn Screening
Developments
Changes to the Down’s Syndrome
Screening Programme
What is screening?
• Screening is a public health service in which
members of a defined population, who do not
necessarily perceive they are at risk of, or are
already affected by a disease or its
complications, are asked a question or offered
a test, to identify those individuals who are
more likely to be helped than harmed by
further tests or treatment to reduce the risk of
a disease or its complications
UK National Screening Committee
Screening for Down’s syndrome
Screening Tests
• Screening tests identify individuals as broadly ‘high’ or ‘low’
chance. High chance results do not indicate that the baby
definitely has Down’s syndrome, but should prompt the
health care professional to offer further screening or
diagnostic tests
Diagnostic Tests
• Diagnostic tests for Down’s syndrome give definite
information on fetal chromosomes by confirming the
presence of a third copy of chromosome 21.
Terminology
Detection Rate (DR)
• The proportion of women who will be identified by the screening test with
an affected pregnancy
False Positive Rate (FPR)
• The proportion of women with a higher chance/screen positive result but
have an unaffected pregnancy
False Negative Rate (FNR)
• The proportion of women who are given a lower chance result but have an
affected pregnancy
Multiples of the median
• The serum marker concentration for a pregnant woman, divided by the
median concentration value for unaffected pregnancies of the same
gestational age
Communicating chance
Screening Markers
First Trimester Serum Markers
Pregnancy Associated Plasma Protein – A (PAPP – A)
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Originates mainly from placental syncytiotrophoblast
Concentration increases with gestation
Screening sensitivity decreases with gestation
Optimal sensitivity at 8 – 9 weeks gestation
Levels reduced in pregnancies affected by Down’s syndrome
First Trimester Serum Markers
Free beta Human Chorionic Gonadotrophin (FßhCG)
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Beta subunit of hCG/intact hCG
Produced by the syncytiotrophoblast cells
Decreases with gestational age
Sensitivity maintained in second trimester
Raised levels in pregnancies affected by Down’s syndrome
Changes to meet new targets and standards
To meet workload standards the four Down’s laboratory
services in Scotland are being reconfigured on to two sites:
• Glasgow (Yorkhill) serving West of Scotland
– Including Highland & Western Isles
• Edinburgh (Western General) serving East of Scotland
– Including Orkney & Shetland
First Trimester Screening
• Pre-test discussion
• Copy of Your Guide to Tests during Pregnancy (48 hrs before
test)
• Sign consent section of SWHMR (woman & midwife)
• Women need to be aware that other conditions may be
identified (Edwards, Patau’s)
• Combined screening offered for all singleton pregnancies
• Multiple pregnancies – NT measurement only
First Trimester Screening
Remember
• Complete ALL sections on form
• CHI mandatory (even if hospital no. still in use)
• Ideally weight should be at time of test, but if booking weight
used MUST be accurate
• Record family origin as per Family Origin Questionnaire
• If known
– record type of assisted conception
– Record age of donor if conceived through egg donation
• Form must be signed by person taking blood sample
• Sonographer MUST record their unique ID code (issued by
lab)
Nuchal Translucency
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Measured between 11 – 13 weeks 6 days
CRL 42 -80 mm
Must be as accurate as possible
Take more than one image and record the
maximum one that meets all criteria
• If not possible to obtain NT measurement offer
return appointment within 3 working days
(provided still in gestational range)
• If unable to obtain measurement at repeat – offer
second trimester screening
First Trimester Screening
• NT measurement combined with results of serum markers
• Results are converted to MoM and corrected for co-variables
including maternal weight, smoking status, and if applicable,
previous affected pregnancy
• NT measurement and blood test performed on same day
• Detection rate – 90%
• False positive rate – 5%
• This test does not screen for neural tube defects and the 18 –
21 week fetal anomaly scan is now the screening test of
choice for these conditions
Second Trimester Serum Screening
Women who book too late for 1st trimester screening will be
offered the quadruple test in the second trimester
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15 weeks + 0 days – 20 weeks + 6 days
Alpha-fetoprotein (AFP)
Human Chorionic Gonadotrophin (Intact hCG)
Unconjugated estriol (uE3)
Inhibin-A
Detection rate – 75%
NB. Abnormal AFP results will continue to be reported
Second Trimester Serum Screening
Remember
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Use specific form for second trimester screening
Complete ALL sections on the form
Clotted samples are required
DO NOT use bottles containing EDTA
Clinical follow up
If the screening test result indicates the woman is in the
“higher chance” group she will be offered counselling and a
diagnostic test
• Amniocentesis – performed between 15 – 20 weeks
• Chorionic villus sampling (CVS) – performed between 11 – 13
weeks
Both of these diagnostic procedures carry a risk of
miscarriage, quoted as 2% for CVS and 1% for amniocentesis
by most hospitals.
Information
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Information needs to be given in a way that helps make it clear to the
parents that the health professional recognises the impact the diagnosis
will have on the parents
• The diagnosis of abnormalities which are perceived by health professionals
as ‘less severe’ than others still cause significant distress for parents
(Statham, Solomou & Green, 2003)
• For parents, the quality of the care they receive is crucial. Few forget their
experience of loss. Most have vivid memories of what happened, what was
done and what was said and these memories may stay with them for
months, years and often a lifetime to come
• For further information go to:
http://fetalanomaly.screening.nhs.uk/CEMT21/
Useful Web Sites
www.pnsd.scot.nhs.uk
www.screening.nhs.uk/
www.fetalanomaly.screening.nhs.uk/
www.dsscotland.org.uk/
www.scotgen.org.uk/
www.healthtalkonline.org/Pregnancy_children/
www.arc-uk.org/