brown prenatal screening for trisomy 21: recent advances and guidelines jacob canick, phd alpert...
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BROWN
Prenatal Screening for Trisomy 21:Recent Advances and Guidelines
Jacob Canick, PhD
Alpert Medical School of Brown UniversityWomen & Infants Hospital
Providence, RI, USA
Department of PathologyMontefiore Medical Center
Bronx, NY
March 17, 2011
Women & Infants’
Grant & Research Support:
- Beckman Coulter, Inc., Brea, CA
- Beckman Coulter Foundation, Brea, CA
- Sequenom, Inc., San Diego, CA
Other:
- Patent Holder – uE3 in prenatal screening
Disclosure Information
Prenatal Screening for Trisomy 21:Recent Advances and Guidelines
1. Brief history of prenatal screening
2. How is screening performance measured?
3. Performance of second trimester, first trimester, integrated, and sequential tests for Down syndrome
4. Guidelines: standard of practice in EUROCAT countries and the United States
5. Trisomy 18 and 13
6. Laboratory issues in prenatal screening
Brief history of prenatal screening
Spina bifida
Anencephaly
The birth prevalence of spina bifida and anencephaly in England and Wales between
1964 and 1975. (N Wald)
Prenatal Screening History Begins with Prenatal Screening for Open Neural Tube Defects using MSAFP
1970s Maternal Serum AFP screening
1980s acceptance in U.S. (ACOG liability alert)
1980s primary prevention with folic acid
2000s move to ultrasound screening?
4 per 1000 births
1970s AFP in maternal serum elevated in NTDs
The birth prevalence of spina bifida and anencephaly in England and Wales between
1964 and 1993. (N Wald)
0.3 per 1000 births
Effect of primary prevention(folic acid)
andprenatal screening
(MSAFP)
Prenatal Screening History Begins with Prenatal Screening for Open Neural Tube Defects using MSAFP
Fetal nucleic acids in maternal plasma?
2011
Integrated 1st and 2nd trim Sequential 1st and 2nd trim
2000
1st trim nuchal translucency (NT) 1st trim NT + PAPP-A + free hCG
1990
1980
Screening using maternal age, offer of amnio 1970
1960 Down syndrome caused by chromosome trisomy
(2009, the 50th Anniversary of discovery by LeJeune)
1950
1940
Down syndrome – maternal age association1930
Prenatal Screening for Aneuploidies:
History2nd trim AFP (with Mat Age)*
2nd trim Multiple markers (Double, Triple, Quad)
Maternal Serum Markers in the 2nd Trimester:Major improvement in screening for Down syndrome
Background
1980s Maternal age as a reason for amniocentesis.
1980s Maternal serum AFP already in use in screening for open NTDs.
1984 Maternal serum AFP is low in Down syndrome pregnancy.
Irwin Merkatz, MDAlbert Einstein Col. Med.
How is screening performancemeasured?
Detection Rate percentage of affecteds called (sensitivity) screen positive by the test
The higher the better!
False Positive Rate percentage of unaffecteds called (1 – specificity) screen positive by the test
The lower the better!
Screening Performance:The challenge in screening is to have a test that has a
high detection rate and low false positive rate.
Performance of second trimester,first trimester, integrated, and
sequential tests for Down syndrome
Advantages:
• Simplest screening method (all serum at one time)
• Includes screening for open NTDs using MSAFP
• Will include a larger proportion of pregnant women
• Follow-up diagnostic test is amniocentesis
0 13 26 40weeks
Screening in the Early 2nd Trimester (15-20 weeks)with Multiple Serum Markers
.1
1
10
Mo
M
AFP inhAuE3
0.74
2.00
hCG
0.61
1.91
2nd Trimester Serum Markers in Down Syndrome Pregnancies
Data from FASTER
Prenatal Screening for Down Syndrome in the Early 2nd Trimester (15 -20 weeks)
0
10
20
30
40
50
60
70
80
90
100
De
tect
ion
Rat
e (
%)
MA + double triple quad ---2nd trimester-----
30%
69% 79%
at 5% false positive rate
59%
81%79%74%
72%
SURUSSFASTER
66%
Advantages:
• Patient privacy
• Earlier diagnosis (if CVS is available)
• Greater availability of pregnancy termination
• Earlier, safer pregnancy termination
0 13 26 40weeks
Screening in the Late 1st Trimester (11-13 weeks)
.1
1
10
MoM
NT f-hCG PAPP-A
1.99 2.29
0.50
F M
alon
e, w
ith p
erm
issi
on
First TrimesterCombined Test:• NT ultrasound
• serum PAPP-A
• serum -hCG
Data from FASTER
0
10
20
30
40
50
60
70
80
90
100
De
tect
ion
Rat
e (
%)
MA + triple quad NT combined 2nd trimester 1st trimester
30% 69% 79% 85%
at 5% false positive rate
64%
Prenatal Screening for Down Syndrome in the Late 1st Trimester (11-13 weeks)
SURUSSFASTERBUN
85% 79%
69% 68% 62%
• Combination of the best markers measured at different times in pregnancy into a single test result.
• This will be more effective than current tests performed at any one time.
PAPP-A + quad markers = SERUM INTEGRATED NT + PAPP-A + quad markers = FULL INTEGRATED
Integrate results into a single risk
0 13 26 40weeks
The Integrated Test:Two Stages to Reach a Single Risk Assessment
Wald NJ et al. N Eng J Med 1999
0
10
20
30
40
50
60
70
80
90
100
Dete
ctio
n R
ate
(%
)
MA + triple quad combined serum full 2nd trimester 1st trimester -integrated-
30%
69%79%
85% 85%94%
89%86%
95%93%
Performance of the Integrated Test
at 5% false positive rate
85%
SURUSSFASTER
0
10
20
30
40
50
60
70
80
90
100
12%
50%60%
66% 66%
85%
De
tect
ion
Rat
e (
%)
at 1% false positive rate
MA + triple quad combined serum full 2nd trimester 1st trimester -integrated-
85% DR at 1%
73%70%
87%86%
72%
SURUSSFASTER
Performance of the Integrated Test
Relative Screening Performance of1st Trimester Combined and Integrated Tests
If 1st Trimester Combined Test Performance is:
DR FPR
Then Full Integrated TestPerformance will be:
DR FPR
85% 5% 94% 5% 90% 2% 85% 1%
90% 5% 96% 5% 93% 2% 90% 1%
90% 2% 96% 2% 93% 1% 90% 0.4%
Is there a way to have both:
earlier screening and diagnosis – as in the 1st trimester test
and
much lower screen positive rate – as in the Integrated Test
YES
Sequential protocols
Sequential Screening: Towards 1st trimester combined or towards integrated, depending on the 1st trimester risk cut-off
2 3 4 570
80
90
100
Full Integrated
First Trimester CombinedSequential protocols
False positive rate (%)
Det
ectio
n ra
te (
%)
Example of Sequential ScreeningPalomaki et al. Obstet Gynecol 2006;107:367-75.
DR FPRStep 1. 1st trimester markers
measured on all women at 10-13 wk. Risk cut-off set at ≥ 1:63 71.8% 1.5%
Step 2. Screen negatives (98.5% of population) have quad markers measured at 15-18 wk. Risk cut-off set at ≥ 1:65 12.5% 0.5%
Overall 84.3% 2.0%
Assumes 1:600 prevalence
Comparing Sequential Screening to 1st Trimester Combined Test and Integrated Test
Palomaki et al. Obstet Gynecol 2006;107:367-75.
Test
1st Trimester Combined
Sequential example
Full Integrated
FPR to get84.3% DR
6.0%
2.0%
1.2%
Sequential Integrated Screeningat Women & Infants (Expected Performance)
Stage 2: • Quad markers• Full Integrated Risk• 1:110 risk cut-off• 31% DR, 1.6% FPR
Stage 1: • 1st trimester markers• PAPP-A and NT• 1:25 risk cut-off• 59% DR, 0.9% FPR
Compare to Integrated Test: 90% DR, 2.0% FPR
Compare to 1st TrimesterTest: 90% DR, 8.0% FPR
Sequential Integrated Test: 90% DR, 2.5% FPR
Prenatal Screening Guidelines:Practice Standards in the United States
American College of Obstetricians and
Gynecologists (ACOG)
January 2007
ACOG 2007
1. “… all women should be offered aneuploidy screening before 20 weeks of gestation, regardless of maternal age.”
2. “… patients seen early in pregnancy should be offered aneuploidy screening that combines first- and second-trimester testing (integrated or sequential).”
3. “The screening strategy chosen will depend on availability of CVS and of personnel trained in NT measurement …”
ACOG Practice Bulletin, No. 77, January 2007
ACOG 2007
4. “When CVS is not available, … offer integrated screening to patients who present in the first trimester … to take advantage of the improved detection rate and low false-positive rate.”
5. “If NT measurement is not available or cannot be obtained …, offer serum integrated screening to patients who present early and second-trimester screening to those who present later.”
ACOG Practice Bulletin, No. 77, January 2007
Trisomy 18 (Edwards Syndrome)and
Trisomy 13 (Patau Syndrome)
1st trim. markerMedian
MoM
NT 2.17
PAPP-A 0.20
Free -hCG 0.25
Trisomy 18: Marker LevelsGE Palomaki 2011, analysis of published literature
2nd trim. markerMedian
MoM
AFP 0.66
uE3 0.36
hCG 0.39
inhA 0.88
PAPP-A 0.10
Modeled Performance
TestDR for
0.1% FPRDR for
0.5% FPR
2nd trim. triple 72 82
1st trim. combined 80 90
Serum integrated 80 89
Full integrated 90 95
Trisomy 18: Screening PerformanceGE Palomaki 2011, unpublished
Actual Performance
Based on clinical trial data, the observed screen positive rate in practice will be higher than the modeling suggests.
Trisomy 13
• 2nd trimester markers are not informative.
• 1st trimester markers are informative.
Their pattern is similar to that found in trisomy 18.
But, published data on trisomy 13 marker levels are biased and too small to estimate their levels with accuracy.
• It is reasonable to assume that the majority of trisomy 13 cases will be identified as part of current trisomy 18 screening protocols that include 1st trimester markers.
Laboratory Issues in Prenatal Screening
• Serum marker assays
• Free -hCG or total -hCG in the 1st trimester
• Screening marker quality assurance
• Nuchal Translucency ultrasound and the laboratory
Prenatal Screening: Serum Assays
Assay type Choices? FDA-approved
2nd trimester:
AFP2 site
immunometric Yes Yes
uE3competitive
immunoassay Yes Yes
-hCG2 site
immunometric Yes Yes
inhibin A2 site
immunometric No Yes
1st trimester:
PAPP-A2 site
immunometric Yes Yes
free -hCG
2 site immunometric Yes/No No
free subunit or hCG itself in the 1st trimester?
Palomaki GE et al. Adv Clin Chem 2007;43:177-210.
free hCG hCG
First Trimester Screening Performance
(NT + serum markers): SURUSS
Wald et al., J Med Screen 2003;10:56-104.
Gest age (weeks)
DR
@ 5
% F
PR
60
65
70
75
80
85
90
95
100
9 10 11 12 13 14
+ PAPP-A
+ PAPP-A + free
+ PAPP-A + hCG
First Trimester Screening Performance
(NT + serum markers): FASTER
Canick et al., Obstet Gynecol 2006;108:1192-9.
Gest age (weeks)
DR
@ 5
% F
PR
60
65
70
75
80
85
90
95
100
10 11 12 13 14
+ PAPP-A
+ PAPP-A + free
+ PAPP-A + hCG
First Trimester Screening Performance(NT + serum markers): Evans meta-
analysis
Evans et al., Am J Obstet Gynecol, March 2007
Gest age (weeks)9 10 11 12
+ PAPP-A
+ PAPP-A + free
+ PAPP-A + hCG
60
65
70
75
80
85
90
95
100
DR
@ 5
% F
PR
• Univariately, free- is a better 1st trimester marker than hCG itself.
• Multivariately, between 11 and 13 gestational weeks, it makes little difference whether free- or hCG is used.
• Because of patent issues in the U.S., most labs currently use hCG in 1st trimester screening.
free subunit or hCG itself in the 1st trimester?
Prenatal Screening Quality Assurance
Applying Serum MarkerQuality Assurance Measuresto Nuchal Translucency (NT)
Marker parameters that are monitored:
Rate of change with may go up or down at a constant increasing gestation rate
Median calculated MoM values should be stable at 1.0
SD of the distribution calculated SD of the log MoM values expected to remain steady
Prenatal Screening MarkersQuality monitoring
log-linear increaseslope = +15% per week
Examples of Marker QA Parameters
MS AFP (MoM)
unaffecteddistribution(x and SD)
(median MoM)
http
://w
ww
.feta
lmed
icin
e.co
m
“normal nuchal translucency” “increased nuchal translucency”
Nuchal Translucency (NT)
Measurement
F M
alon
e, w
ith p
erm
issi
on
NT parameters that are monitored:
Rate of increase with CRL log-linear over 10,3 - 13,6 weeksshould 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
1st Trimester Nuchal Translucency (NT)Quality monitoring
log-linear increaseslope = +15% per
week
log-linear increaseslope = +20% per week
Maternal Serum AFP
Increases with
Increasing Gestation
Nuchal Translucency
Increases with
Increasing Gestation
Schuchter et al, Prenat Diagn 1998
UK SURUSS Trial: NT measurement (mm)in 75 pregnancies with Down syndrome according to
CRL
Wald NJ et al, Health Technology Assessment 2003; Vol. 7: No. 11
NT in Down Syndrome
Overlapping Distributions: First Trimester Markers
NT
PAPP-A
f-hCG
affected
unaffected
affected
affectedunaffected
unaffected
MS AFP (MoM)
NT (MoM)
NT
AFPSD of log MoM = 0.15
The Distribution of AFP and NT MoM
in Unaffected Pregnancies
SD of log MoM = 0.10
MS AFP (MoM)
NT (MoM)
NT
hCG
0.2 10hCG (MoM)
The Distribution of hCG and NT MoM
in Unaffected Pregnancies
SD of log MoM = 0.23
SD of log MoM = 0.10
Why is NT such a good marker?
0.2 0.5 1 2 5 10NT (MoM)
0.2 0.5 1 2 5 10hCG (MoM)
unaffected
unaffected DS
DS
NT: 0.11 SD50% DR 1% FPR
hCG: 0.24 SD
50% DR 8% FPR
Crossley JA et al. BJOG 2002;109:667-76.
Inter-operator variation at one hospital
Range of NT measurements (in MoM) between hospitals
Published Literature:Variation in NT median measurement
Schielen PC et al., Prenat Diagn 2006;26:711-8
Published Literature:Variation in NT median measurement
FMF median equation
FMF-certified centers
Non-FMF certified
Palomaki GE et al. Genet Med 2008;10(2):131-138
“Laboratories should routinely monitor the quality of nuchal translucency measurements… When possible, instituting sonographer-specific medians and providing individualized feedback about performance and numbers of women tested offer the potential to yield more consistent and improved performance.”
NT monitoring: when to make changes
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
Nick Wald
University of London
Primary collaborators over many years
JimHaddow
GeorgeKnight
GlennPalomaki
GeralynLambert-Messerlian
---------Women & Infants Hospital - Brown University---------