Epidemiological Monitoring and
Quality Control of Nuchal Translucency
Jack Canick
Intensive Course on Screening for Down’s Syndrome
Wolfson Institute of Preventive Medicine
London
May 2013
Women & Infants’
BROWN
NT Training Programs
Fetal Medicine Foundation
Less formalized systems
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
The Level of Maternal Serum AFP Increases
with Increasing Gestation
log-linear increase
slope = +15% per week
Palomaki GE, unpublished data
Nuchal Translucency Thickness Increases
with Increasing Gestation
log-linear increase
slope = +20% per week
Schuchter et al, Prenat Diagn 1998; 18: 281-4
AFP
SD of log MoM = 0.15
MS AFP (MoM)
The Distribution of
AFP and NT MoM
in Unaffected
Pregnancies
NT
SD of log MoM = 0.10
NT (MoM)
Why is NT such a good marker?
unaffected
NT: 0.11 SD
DS
0.2
0.5
1
2
NT (MoM)
0.5
5
10
DS
unaffected
0.2
50% DR
1% FPR
1
2
hCG (MoM)
5
hCG: 0.24 SD
10
50% DR
8% FPR
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
calculated SD of the log MoM
values expected to be about 0.1
NT medians by CRL: All Centers
NT change with gestation
NT medians by CRL: All Centers
median MoM
Distribution width
Epidemiologic Monitoring of Nuchal Translucency:
Monthly Medians - A
Epidemiologic Monitoring of Nuchal Translucency:
Monthly Medians - B
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
Getting started:
Newly 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
New sonographer A
NT (mm)
Reference (slope +20% per week)
New sonographer A
+14%
1
30
40
50
60
CRL (mm)
70
80
Sonographer variation:
New sonographer B
NT (mm)
Reference (slope +20% per week)
New sonographer B
+48%
1
30
40
50
60
CRL (mm)
70
80
Sonographer challenges:
New sonographer C
NT (mm)
3
Reference
Reference(slope
(slope+20%
+20%per
perweek)
week)
New
Newsonographer
sonographerBC
?
1
30
40
50
60
CRL (mm)
70
80
Published Literature:
Variation in NT median measurement
FMF-certified centers
Non-FMF certified
Schielen PC et al., Prenat Diagn 2006;26:711-8
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 2002;109:667-76.
NT Epidemiologic Monitoring
NT Medians (mm) at 15 FASTER Centers
3.0
2.7
2.4
2.1
1.8
NT (mm)
1.5
1.2
0.9
0.6
0.3
10
11
12
G.A. (week)
13
14
NT Epidemiologic Monitoring
Impact of Using A Single Population Median
NT (mm)
Example of a 30 year old who has the most typical result at 12 wks
3.0
2.7
2.4
2.1
1.8
1.5
Center A is routinely high:
result
1.3mm
=
= 1.67 MoM
median
0.8mm
risk: 1 in 230
1.2
Center B is routinely average:
0.9
result
0.8mm
=
median 0.8mm
0.6
= 1.00 MoM
risk: 1 in 2400
Center C is routinely low:
0.3
10
11
12
13
G.A. (week)
14
result = 0.6mm = 0.75 MoM
median 0.8mm risk: 1 in 3500
Patient-specific risk varies 15 fold.
NT Epidemiologic Monitoring
Impact of Using Center-Specific Medians
NT (mm)
Example of a 30 year old who has the most typical result at 12 wks
3.0
2.7
2.4
2.1
1.8
1.5
Center A is routinely high:
result
1.3mm
=
= 1.00 MoM
median
1.3mm
risk: 1 in 2400
1.2
Center B is routinely average:
result
0.8mm
=
= 1.00 MoM
median 0.8mm
risk: 1 in 2400
0.9
0.6
0.3
10
11
12
13
G.A. (week)
Center C is routinely low:
result = 0.6mm
= 1.00 MoM
14 median
0.6mm
risk: 1 in 2400
Patient-specific risk is the same at each center.
Palomaki GE et al. Genet Med 2008;10(2):131-138