Update Non Invasive

Prenatal TestingLauren Lynch, MD

Maternal Fetal Medicine and Clinical Genetics

Agenda

Risk of Aneuploidy

First Trimester Screening

Second Trimester Screening

Cell Free DNA in Maternal Blood

Expanded carrier screening

Risk Of Aneuploidy

Risk related to

maternal age

gestational age

prior history

ART?

Risk not related to paternal age

Risk of Down Syndrome by

maternal age

First Trimester Screening

Screens for Trisomy 21 and 18, although other

aneuploidies may be detected

Utilizes Nuchal Transluscency measurement ,

PAPP-A and HCG

10+3-13+6 weeks (CRL 39-84mm)

Detects 85% of Trisomy 21 and 90% Trisomy

18

Nuchal Transluscency

Nuchal Transluscency

Nuchal Translucency

The hypoechoic region located between the skin

and soft tissues behind the cervical spine

Presumed to represent mesenchymal edema

and is often associated with distended jugular

lymphatics

Although NT increases with gestational age, an

NT >3.5mm is abnormal at any GA

NT increases the risk of aneuploidy, cardiac

anomalies and other genetic defects

NT Measurements

Only NT measurements made by

practitioner/sonographer certified by

Nuchal Transluscency Quality Review

Quality (NTQR)accepted by qualified

labs (ntqr.org)

Ongoing quality monitoring by NTQR

First Trimester Screening

Serum Screening: PAPP-A/free B-HCG

(Ultrascreen®)

65% detection Down Syndrome

Combined Test: NT and PAPP-A/ B-

HCG (First Screen®)

85% detection Down Syndrome

Second Trimester Screening

15+0 to 20+6 weeks

Triple Screen: AFP, HCG, Estriol

Quadruple Screen: AFP, HCG, Estriol,

InhibinA

Down Syndrome Detection

Rate at a 5% FPRFIRST TRIMESTER

Serum alone (Ultrascreen) 65%

Combined Test(First Screen) 85%

SECOND TRIMESTER

Triple Screen 65%

Quadruple Screen 80%

First and Second Trimester

Screening: Possible Test

CombinationsIntegrated Testing: Combined test, no disclosure

regardlessQuadruple test (MOST SENSITIVE AT

LOWEST FALSE POSITIVE RATE)

Sequential Testing: Combined testHigh riskoffer CVS,

Not high riskquadruple test

Contingent Testing:Combined test

High riskoffer CVS,low riskno more testing,

intermediate riskquadruple test

Fetal DNA in maternal blood

Cell free DNA (cfDNA)

3-13% of cell free DNA in maternal blood is fetal (“fetal fraction”)

Mostly placental in origin

Half life is minutes

Can be detected as early as 5 weeks and consistently by 9 weeks

≈ 98% accurate in predicting fetal sex

cfDNA in Maternal Blood

Screening only for Trisomy 21, 18 ,13

Optional screening for sex chromosome abnormalities (and sex determination)

Sensitivity Tri 21 >98%

False Positive rate <0.5%

Obesity (BMI>30): less cfDNA : more often test not possible

Multiple pregnancies: less reliable

cfDNA: Positive Predictive

Value

PPV depends on prevalence of the disease

Ex: A 40y/o patient with a positive test for Tri 21

has a 87% chance of having a fetus with Tri 21 vs.

33% if she is 25y/o

Positive predictive value should be reported for

each patient with a positive result (some labs do

not)

TOP should never be done based on cfDNA results

without confirmation by CVS or amniocentesis

cfDNA: False Positives

May be caused by:

Limitations of the technology

Vanished twin

Confined placental mosaicism

Maternal malignancy

cfDNA: “No Result”

If fetal fraction is low the test is less accurate

Most labs will not report the results if fetal

fraction is less than 4%

Reasons for low fetal fraction are: high BMI,

early GA and aneuploidy

Women with “no results” are at higher risk of

having a fetus with aneuploidy (as high as 23%)

and should receive genetic counseling

cfDNA vs. First Trimester

ScreenFirst Screen

Sensitivity Tri 21 85%

False Positive 5%

May detect other

abnormalities such as

cardiac defects

May detect other

chromosome abnormalities

Cost: ≈ $250

cfDNA

Sensitivity Tri 21 > 98%

False Positive <0.5%

Only detects Trisomy

21,18,13 (optional sex

chromosomes)

Only detects aneuploidies

sought for

Cost: >$500

cfDNA vs. Invasive testingcfDNA

Sensitivity Tri 21/18/13

98%

50% of aneuploidy are other

than the above

False Positive< 0.5%

No testing related losses

Decreases number of invasive

tests required

Cost: similar to invasive

CVS/Amniocentesis

Sensitivity all aneuploidy 100%

False positive: 0%

Procedure related risk: 1:1000

n/a

Cost: similar to cfDNA

ACOG Committee Opinion

NIPTDecember 2012

cfDNA is an option as primary screening for women at increased risk of aneuploidy

Counseling regarding limitations of cfDNA recommended

cfDNA is not currently recommended for low risk women

ACOG &SMFM Committee

Opinion

September 2015“Given the performance of conventional

screening methods, the limitations of cell-free

DNA screening performance, and the limited data

on cost- effectiveness in the low-risk obstetric

population, conventional screening methods

remain the most appropriate choice for first-line

screening for most women in the general obstetric

population”

Committee Opinion (cont)

All women with positive cell free DNA testing should

be offered diagnostic testing

Cell free DNA testing not recommended in multiple

gestations

Routine cell free DNA testing for microdeletion

syndromes not recommended

Women with “uninterpretable” or “inconclusive”

results should be counselled and offered diagnostic

testing

SMFM Dec 2015

Expanded Carrier Screening

Expanded Carrier Screening

Each one of us is a carrier of 4-5 recessive

mutations

If a couple carries a mutation in the same gene

their offspring have a 25% of being affected

Until now carrier screening was based on

ethnicity

Ethnicity is increasingly difficult to determine

Expanded Carrier Testing

Current technology allows for screening of a large

number of conditions simultaneously

Most labs test for >100 diseases mostly autosomal

recessive and some X-linked

Targeted mutations are sought: not all mutations

There is a residual risk

Ideally performed before pregnancy

Can be done sequentially

Pretesting counseling should be offered

Expanded Carrier TestingExamples of diseases tested

Cystic fibrosis

Congenital adrenal hyperplasia

Sickle Cell and thalasemias

Familial dysautonomia

Fragile X

PKU

Expanded carrier testing

Carrier screening does NOT

replace newborn screening for

genetic diseases

Expanded carrier screening

Carrier Frequencies>23,000 patients

Counsyl

108 recessive diseases

24% individuals carriers for at least 1 mutation

6% carriers for 2 or more mutations

Most common mutations Alpha antitripsin, cystic fibrosis, SMA, Smith Lemli Opitz, Sickle/B thal

76% of mutations would have been missed by ACOG carrier screening guidelines

Lazarin,et al:GenetMed,2013

ACOG,SMFM &ACMG

Statement ECS

March 2015Does not replace current screening guidelines published

by individual organizations

Patients with a positive family history of a genetic

condition, genetic counseling is indicated for accurate

risk assessment and to ensure the most specific carrier

test is offered

Exceptions: Hemoglobinopathy screening should still be

done by MCV and Hgb electrophoresis and Tay Sachs

by hexosamidase A

ACOG Statement cont.Providers should choose a lab that tests for diseases that

are:

Associated with Cognitive disability

Need for surgical or medical intervention

Effect on quality of life

Prenatal diagnosis possible

May choose not to screen for:

Adult onset diseases

Mild phenotypes (ex MTHFR)

Non Invasive Testing for fetal

aneuploidy: Summary

First Trimester testing is preferred

For high risk patients First Screen, cfDNA, and

Invasive testing are options

Low Risk patients First Screen or if FS not possible

,Quadruple Screen ,cfDNA may be offered

Invasive testing should be available irrespective of age

and insurance coverage

First trimester serum screen (Ultrascreen) and Triple

Screen are no longer adequate

Summary (cont)

cfDNA is a screening test (NOT diagnostic)

which is better than First Screen in detecting

Trisomy 21,18 &13, but does NOT replace

invasive testing since 50% of aneuploidies are

not the common trisomies and would not be

detected by cfDNA

Expanded Carrier Screening:

Summary

Patient with family history of genetic disease(a

priori risk) should receive genetic counseling

Patients without family history may be tested by

ACOG guidelines or expanded screening

although there are some advantages to the later

Exception: hemoglobinopathies and Tay Sacks

2nd Trimester Screening for DS

AFP HCG Estriol Inhibin

Tri 21 ↓ ↑ ↓ ↑

Tri 18 ↓ ↓ ↓ ↓

NTD ↑

First trimester screening for DS

PAPP-a B-HCG NT

Tri 21 ↓ ↑ ↑

Tri 18 ↓ ↓ ↑