Epidemiological Monitoring and Quality Control of Nuchal Translucency

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Epidemiological Monitoring and Quality
Control of Nuchal Translucency

• Jack Canick

Intensive Course on Screening for Downs
Syndrome Wolfson Institute of Preventive
Medicine London May 2013
BROWN
Women Infants
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NT Training Programs

• Fetal Medicine Foundation

Less formalized systems
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Overview

• Epidemiological monitoring is the study of the
  measurements made on the population being tested
• Application of serum marker experience to nuchal
  translucency monitoring
• Examples of monitoring activities for nuchal
  translucency
• New sonographer data

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The Level of Maternal Serum AFP Increases with
Increasing Gestation
Palomaki GE, unpublished data
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Nuchal Translucency Thickness Increases with
Increasing Gestation
log-linear increase slope 20 per week
Schuchter et al, Prenat Diagn 1998 18 281-4
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SD of log MoM 0.15
The Distribution of AFP and NT MoM in Unaffected
Pregnancies
SD of log MoM 0.10
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Why is NT such a good marker?
NT 0.11 SD
50 DR
1 FPR
hCG 0.24 SD
50 DR
8 FPR
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Nuchal Translucency (NT) Epidemiological
monitoring
NT parameters that are monitored Rate of
increase with CRL log-linear over 10,3 - 13,6
weeks should go up by 20 per
week Median calculated MoM values should be
stable at 1.0 MoM SD of the distribution calcula
ted SD of the log MoM values expected to be
about 0.1
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NT medians by CRL All Centers
NT change with gestation
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NT medians by CRL All Centers
median MoM
Distribution width
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Epidemiologic Monitoring of Nuchal Translucency
Monthly Medians - A
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Epidemiologic Monitoring of Nuchal
Translucency Monthly Medians - B
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NT data monitoring

• Use objective criteria as guide
• Partially subjective process
• Look for trends
• Sample volume must be considered
• What to do with very small volume sonographers?
• Sonographer feedback has been minimally useful

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Getting startedNewly trained sonographers

• Provide paired CRL and NT measurements to the
  laboratory
• If more than one sonographer within a center,
  identify each person within the database
• Expect data to conform to parameters defined in
  literature

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New sonographer A
Reference (slope 20 per week) New sonographer A
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NT (mm)
1
30
40
50
60
70
80
CRL (mm)
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Sonographer variationNew sonographer B
Reference (slope 20 per week) New sonographer B
48
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Sonographer challengesNew sonographer C
Reference (slope 20 per week) New sonographer C
Reference (slope 20 per week) New sonographer B
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?
NT (mm)
1
30
40
50
60
70
80
CRL (mm)
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Published Literature Variation in NT median
measurement
FMF-certified centers Non-FMF certified
Schielen PC et al., Prenat Diagn 200626711-8
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Published Literature Variation in NT median
measurement
Range of NT measurements (in MoM) between
hospitals
Inter-operator variation at one hospital
Crossley JA et al. BJOG 2002109667-76.
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NT Epidemiologic MonitoringImpact of Using A
Single Population Median
Example of a 30 year old who has the most typical
result at 12 wks
Center A is routinely high result
1.3mm median 0.8mm Center B is routinely
average result 0.8mm median
0.8mm Center C is routinely low result
0.6mm median 0.8mm

1.67 MoM
risk 1 in 230

1.00 MoM
risk 1 in 2400

0.75 MoM
risk 1 in 3500
Patient-specific risk varies 15 fold.
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NT Epidemiologic MonitoringImpact of Using
Center-Specific Medians
Example of a 30 year old who has the most typical
result at 12 wks
Center A is routinely high result
1.3mm median 1.3mm Center B is routinely
average result 0.8mm median
0.8mm Center C is routinely low result
0.6mm median 0.6mm

1.00 MoM
risk 1 in 2400

1.00 MoM
risk 1 in 2400

1.00 MoM
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risk 1 in 2400
Patient-specific risk is the same at each center.
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Palomaki GE et al. Genet Med 200810(2)131-138