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Genetic Testing in Pregnancy
Johanna Warren, MD
OAFP Women’s Health Winter Conference
January 19, 2014
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What genetic screening test do
you routinely offer your patients?
A.
B.
C.
D.
E.
F.
Quad/Penta screen
Integrated Screening
Nuchal Translucency (NT) only
Stepwise Sequential Screen
NIPT (cffDNA)
none
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Learning Objectives
 Use
the concepts of pre-test probability,
positive and negative predictive values as they
apply to testing for fetal aneuploidy.
 Outline
advantages and disadvantages of
various approaches to first-trimester and
second-trimester screening as well as invasive
diagnostic testing for Down syndrome.
 Discuss
emerging cell-free fetal DNA (cffDNA)
technology and review indications for use in
screening.
 Summarize
the current recommendations for
cystic fibrosis screening.
+ Statistics
 Pre-test
probability
Prevalence of the disease
 Post-test probability after one or more preceding tests
 Rough clinical estimation

 Positive
predictive value (PPV)
the likelihood that an individual with a positive test result
truly is affected/has the genetic condition
 inherently dependent upon the prevalence

 Negative
predictive value (NPV)
the likelihood that an individual with a negative test result
is truly unaffected/does NOT have the genetic condition
 measure of test accuracy

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What Makes a Good Screening Test?

The condition should be an important health problem.

There should be an acceptable test for the condition.


High sensitivity to detect not yet clinically detectable condition
High specificity to minimize false positives

The test should be available to the population.

The test should be affordable.

There should be acceptable treatment for the condition.
 There
should be a “latent stage” of the disease, allowing for
detection/testing before a critical point, during which
treatment would be optimal.
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What is the purpose of antenatal
genetic testing?
 Assess
risk for chromosome abnormalities
 particularly
 Determine
Down syndrome & Trisomy 18
which pregnancies should be
offered invasive prenatal diagnosis
+ Who Should Be Screened?
 ACOG
Practice Bulletin (2007)
 All
pregnant women, regardless of their age,
should be offered screening and diagnostic
testing for aneuploidy.
 Women should be counseled regarding the
differences between screening and invasive
diagnostic testing.
 Ideally, patients
seen early in pregnancy
should be offered screening that combines
1st and 2nd trimester testing
 Screening
test chosen will depend on availability
of NT US as well as CVS
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Testing for Fetal Aneuploidy –
Focus on Down Syndrome
(trisomy 21)

Explosion of available screening tests

Detection of Down Syndrome 90+% with non-invasive screening
tests

Confirmation diagnosis still requires invasive testing

Amniocentesis

Chorionic villus sampling
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Quick Review
 Several
methods for combining first- and
second-trimester screening reach higher
detection rates for Trisomy 21 than either
first- or second-trimester screening alone.
 Common
options:
 Ultrasound:
Nuchal Translucency
 Integrated Screenings
 Quadruple/Penta Marker Screenings
 Stepwise Sequential Screening
+ First Trimester - Ultrasound
 Nuchal Translucency
(NT)
Normal: 1-3mm
 Increased NT is an indication of a chromosomal
abnormality, single gene defect, or birth defects
(commonly cardiac defects)

 Nasal

Bone
Absent/hypoplastic in 70% T21
 Ductus Venosus

Detection rate 75%, FPR 5%
 Tricuspid

– reversed a-wave flow
Regurgitation
Detection rate 67.3% in T21, FPR 5.2%
+ Integrated Screenings
 Integrated
Screening
 Ultrasound
for Nuchal Translucency (NT) + serum
PAPP-A/hCG analysis between 10-13.6wks GA;
results of these tests are HELD
 Serum quad screen test between 15 -19 wks GA
 At that time, the results of all the studies, combined
with risk assessment due to the patient's age, are
used to present a single-risk figure
 Serum
Integrated Screening
 first-trimester
serum PAPP-A/hCG test result is
combined with a second-trimester quad screen test
to provide a single-risk figure (no NT US)
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Quadruple Marker Screening
 Measure
raw values of:
 AFP
(alpha fetoprotein)
 ue3 (unconjugated estriol)
 hCG (human chorionic gonadotropin)
 DIA (dimeric inhibin A)
 Compare
to median value for the appropriate
gestational age (MoM)
 Valid
between 14-22.9 weeks GA (optimal 1618wks); risk of NTD not provided for samples
collected prior to 15 weeks.
+ Stepwise Sequential Screening
 First Trimester
NT US + serum PAPP-A analysis between 10-13.6wks
GA
 Results combined with the patient's age-associated
risk,
 Patient is given a risk assessment for aneuploidy
 may choose at this time to undergo invasive testing
(e.g., amnio or CVS), or add quad screen test at 15-19
wks GA

 Second Trimester
Quad screen test at 15-19 wks GA
 a new risk is assessed based on the results of patient’s
age and both the first- and second-trimester screening
test results

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Sequential Screening
 How
do you decide when to proceed with
invasive testing?
 Risk


chorionic villus sampling (CVS) ~ 0.5-1/100
amniocentesis ~1/1000
 After



of miscarriage (approximate; operator-specific)
1st trimester results return:
If risk is greater than ~1 in 50, offer CVS
If risk is less than ~1 in 1,000, advise no further testing is
necessary.
If risk is between these two (arbitrary) cutoffs, offer quad
screen test after 15 wks GA, and determine a new risk
assessment
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FASTER Trial Data
Screening Test
Best Detection
Rate for Down
Syndrome
NT alone
70%
Quad screen alone (2nd trimester)
81%
First Screen (with NT)
87%
Serum Integrated (1st tri PAPP-A/hcg + 2nd tri
quad)
88%
Sequential Screen (1st tri PAPP-A + NT + 2nd tri
quad)
94%
Integrated Screen (1st tri PAPP-A/hcg + NT + 2nd tri 96%
quad); patient does not receive results until 2nd
trimester testing complete
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What do you do with…
 Normal
 Other
Ultrasounds
Abnormal Serum Studies
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Normal Ultrasounds
 Normal
ultrasound: 50-60% decrease in
risk for chromosome abnormalities
 Remember
that at least 30% of fetuses with
Down syndrome have NO abnormal
ultrasound findings!
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Low 1st Trimester PAPP-A

Pregnancies with PAPP-A of ≤ 5%tile (0.4MoM) are at
increased risk for:

Spontaneous fetal loss < 24 wks GA

Low birth weight

Preeclampsia

Gestational HTN

Preterm birth and stillbirth

Preterm premature rupture of membranes

Placental abruption
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Abnormal 2nd Trimester Serum
Values
Elevated hcg
Elevated inhibin-A
Low uE3
preeclampsia
preeclampsia
steroid sulfatase deficiency
preterm delivery
IUGR
Smith-Lemi-Opitz syndrome
low birth weight infant
preterm delivery
congenital adrenal
hyperplasia
IUFD
adrenocorticotropin
deficiency
placental abruption
hypothalamic corticotropin
deficiency
anencephaly
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What’s next?
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Cell-free Fetal DNA (cffDNA)

Screening or Diagnosis?

Known as “Noninvasive Prenatal Testing” or “NIPT”

Technology uses circulating cell free fetal DNA found in the
maternal plasma

Thought to be derived primarily from placenta

New recognition of limitations of screening with pregnancies with
placental mosacisms

Unclear data for egg donor pregnancies

Available as early as 10th week of pregnancy

Cleared from maternal blood almost immediately after childbirth
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Cell-free Fetal DNA (cffDNA)

2012 publications (Sparks et al., Ashoor et al., Bianchi et al.)

targeted (chromosome-selective) sequencing of chromosomes 18
and 21

highly accurate

potentially more cost-effective

Technology can be expected to identify 98% of cases of T21
with a false-positive rate of < 0.5%.

Multiple different labs

MaterniT21plus by Sequenom

Verifi by Verinata

Harmony by Ariosa
+ Cell-free Fetal DNA (cffDNA) Labs



MaterniT21plus by Sequenom

>99% detection for T21, T18

~90% detection for T13

<1% false positive rate

Cost: $235-2700
Verifi by Verinata

>99% detection for T21, T18

~80% detection for T13

>90% detection for 45,X

<1% false positive rate
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Cost: $200-1200
Harmony by Ariosa

>99% detection for T21, T18

~80% detection for T13

<1% false positive rate

Cost: up to $795
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Cell-free Fetal DNA (cffDNA)

ACOG Committee Opinion, Dec. 2012 – “Noninvasive
Prenatal Testing for Fetal Aneuploidy”

cffDNA testing should be an informed patient choice after
counseling and should not be part of routine prenatal laboratory
assessment.

cffDNA testing should not be offered to low-risk women or women
with multiple gestations (has not been studied).

A negative cffDNA test result does not ensure an unaffected
pregnancy.

A patient with a positive test result should be referred for genetic
counseling and should be offered invasive prenatal diagnosis for
confirmation of test results.
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Indications for Considering Use of
cffDNA for Screening

Maternal Age ≥ 35 years at delivery

Fetal ultrasound findings indicating increased risk of aneuploidy




CPCs?
IEF?
Clinodactyly?
Absent/hypoplastic nasal bone?

History of a prior pregnancy with a trisomy

Positive test result for aneuploidy (any serum test)

Parental balanced translocation with increased risk of fetal
trisomy 13 or 21.
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+ Considerations
 Primary
insurers are generally reimbursing
for first-trimester screenings, including NT
ultrasounds as well as NIPT.
 Are
there referral sites available to your
patients for appropriate genetic counseling
and NT US measurements? What about for
CVS and/or amniocentesis?
 What
testing strategy makes the most sense
for your patients?
 How
do you see it evolving in the next 1-2
years?
+ Testing for Cystic Fibrosis (CF)
 Site
of genetic defect = CF Transmembrane
Regulator (CFTR) gene, a chloride channel protein

~ 1700 mutations of CFTR gene have been described
 Disease
incidence: 1 in 2500 in the non-Hispanic
white population
 Carrier
frequencies:
1/24-25 Caucasians of European descent or
Ashkenazi Jews
 1/58 Hispanic American
 1/61 African American
 1/94 Asian American

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CF Genetic Testing
 Difficult
to assign a single ethnicity to
individuals
 ACOG
2011 Recommendation – offer CF
carrier screening to all women of
reproductive age
 Need
to be screened only once
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
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CF Parental Genetic Testing
Sequential testing

Test mother for carrier state

If positive, test father
Concurrent testing
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Test mother and father simultaneously
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Advantage: can be done prior to conception

Limitation: depends on accurate ID of father
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If both parents are unaffected but family hx of CF exists:

Genetic counseling

Identify if CFTR mutation analysis in affected family member is available
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Positive CF Testing

If both parents are carriers…

and prior to conception


offer ART options for diagnosis of embryo
and currently pregnant

offer CVS or amnio to confirm status of fetus

No in-utero treatments exist

Variable clinical scenarios, with median survival for patients
37yrs
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“Residual Risk”

Potential risk of having an affected child with CF after
testing is completed and is negative

Varies by race and current testing panel for gene
abnormalities

Will vary over time and by laboratory

Newborn screening panels that include CF screening
do not replace maternal carrier testing
+ Summary Recommendations

Genetic screening in pregnancy (and pre-conception!) is
rapidly getting more complex.

OHSU Online Course (FREE!)

0.5 CME credits available

www.ohsu.edu/prenatal-screening
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Understand your patient population and your local
capabilities, specifically as they relate to genetic counseling,
ultrasound expertise, and diagnostic testing.

Develop practice workflows that allow women to access
early genetic screening should they desire.
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