GENETIC TESTING IN PREGNANCY:WHAT ARE THE OPTIONS?Christy M. Isler, MD

East Carolina University

DISCLOSURE INFORMATIONGENETIC TESTING IN PREGNANCY: WHAT ARE THE OPTIONS?

CHRISTY ISLER, MD

• I have no financial relationships to disclose

• I will not discuss off label use and/or investigational use in my presentation

LECTURE DESCRIPTION

A review of screening and diagnostic testing for common genetic abnormalities in pregnancy

OBJECTIVES

A review of screening and diagnostic tests for common genetic abnormalities in pregnancy

1. Discuss conventional genetic screening tests used in the first and second trimester

2. Discuss genetic testing with cell free fetal DNA test

3. Discuss diagnostic genetic testing and the associated invasive procedures

4. Discuss first and second trimester ultrasound markers for aneuploidy

INDIVIDUALIZED RISK

• Every woman has the right to pursue or decline screening or diagnostic tests

• Discuss individualized risk

• Beyond “low” risk versus “high” risk

• Counseling re: aneuploidy screening,

• Benefits and risks of diagnostic and screening test

• How accurate are the tests

CHROMOSOMAL ABNORMALITIES

CHROMOSOMAL ABNORMALITIES

• Aneuploidy

Triploidy

Mosaicism

Abnormal structures

Deletions/duplications

Translocations

CHROMOSOMAL ABNORMALITYPREVALENCE

• Live births: 1 in 150

• Early embryonic death 60-70%

• First trimester miscarriage 50%

• Stillbirths 5%

• Most common autosomal trisomy

• Down syndrome

• Most common sex chromosome aneuploidy

• Klinefelter syndrome 47,XXY- 1in 500 males

• Turner syndrome 45,X

ANEUPLOIDY RISKS FACTORS

• Increasing maternal age

• Prior affected child

• Not increased with 45,X or 47,XYY

• Parental translocation—picture of karyotype

• + screening test

• Ultrasound abnormalities

DOWN SYNDROME

• Most common form inherited intellectual disability

• 1 in 800 live births

• 95% nondisjunction

• Remainder translocation or mosaicism

• 40% fetal loss between first trimesterterm

WHY IS MATERNAL AGE NOT ENOUGH?

Maternal age >35 years = 22% detection rate Down syndrome

WHICH TEST TO CHOOSE?

• Desire for information

• Prior obstetrical history

• Family history

• Number of fetuses

• Gestational age at presentation

• Available NT services

• Are measurements obtained

• Test sensitivity and specificity

• Cost

• Care of an affected child

• Options for pregnancy continuation

“TRADITIONAL” OR “CONVENTIONAL”SCREENING TESTS

FIRST

SECOND

COMBINED

FIRST TRIMESTER SCREENING

• ANALYTES

• Serum HCG (free Beta or total) AND PAPP-A

• NUCHAL TRANSLUCENCY

• CRL 45mm - 84mm

• Maternal age, prior aneuploidy, weight, race, #fetus

• Detection rate 82-87%, screen positive rate 5%

• 11 weeks optimal Down syndrome detection

NT US

1. NT margins are clearly visualized

2. Fetus in a midsagittal plane

3. Appropriate imaged magnification

4. Fetal neck in neutral position

5. Visualize amnion separate from NT line

NT US

6. +Calipers used to perform measurements

7. Proper caliper placement

8. Calipers perpendicular to long axis of fetus

9. Measure at widest NT space

2ND TRIMESTER SCREENING

• 150-226 (16-18 best for ONTD)

• QUAD • Hcg, AFP, dimeric inhibin A, uE3

• PENTA• add hyperglycosolated Hcg

• Age, weight, race, diabetes, #fetus

• No special ultrasound

COMBINED SCREENING

• Sequential screening• Stepwise

•Contingent

• Integrated screening• Serum integrated screening

SEQUENTIAL SCREENINGSTEPWISE

1st Analyte + NT

Low risk

2nd

trimester analyte

Final results

High risk

(CVS/

amnio)CffDNA

SEQUENTIAL SCREENINGCONTINGENT

1st Analyte + NT

Low risk

Done

High risk

Diagnostic

(CVS/amnio)CffDNA

Intermediate

2nd trimester analytes

INTEGRATED SCREENING

1st analyteand NT

2nd

analyte

High risk

Amnio CffDNA

SERUM INTEGRATED SCREENING

1st analyte

2nd analyte

High risk

Amnio CffDNA

Test Down syndrome

Detection rate(%)

Screen

positive(%)

Early results? ONTD screen? NT US?

First trimester

screen

82-87 5 Yes No Yes

Second

Trimester

screen

81 5 No Yes No

COMBINED TESTS

Sequential -

stepwise

95 5 Yes Some Yes

Sequential –

Contingent

88-94 5 Yes Yes Yes

Integrated 96 5 No Yes Yes

Serum

integrated

88 5 No Yes No

1ST AND 2ND TRIMESTER SCREENING

ADDITIONAL BENEFITS

1ST TRIMESTER SCREENING

• Increased NT >3.0mm or >99th centile OR cystic hygroma

• Genetic syndromes

• Isolated anomalies

• Heart

• Abdominal wall

• Diaphragmatic hernia

• Offer genetic testing, ultrasound, fetal echocardiogram

UNEXPLAINED ABNORMAL ANALYTES

• Abnormal analytes with no structural anomalies• Elevated hCG• Elevated AFP• Elevated dimeric inhibin A

• Increased risk • fetal death• IUGR• Preeclampsia

• Low maternal serum estriol• Smith-Lemli-Opitz syndrome• Placental steroid sulfatase deficiency

CELL FREE FETAL DNANIPT

NIPS

CELL FREE FETAL DNA

• Short segments of DNA in maternal blood

• Released from placental cells undergo apoptosis

• Cleared from maternal circulation within hours of childbirth

• Multiple methods-performance similar

CELL FREE FETAL DNADETECTION

• Down syndrome 99% detection rate

• Screen + rate 0.5% (women with reportable results)

• Advantage is lower false positive rate with less invasive procedures

• Detection lower for other aneuploidies

• Trisomy 18 – 97%

• Trisomy 13 – 87%

• Sex chromosome abnormalities

CELL FREE FETAL DNALOW FETAL FRACTION

• <10 weeks

• Increased BMI

• 250 pounds-10% low fetal fraction estimated

• Fetal aneuploidy

• “no call” <4-8%

• No call, indeterminate, uninterpretable, low fetal fraction

• Repeat 40% no call

CELL FREE FETAL DNAPOSITIVE TEST

• Fetal aneuploidy

• Confined placental mosaicism

• Resorbing twin

• Maternal malignancy

• Maternal aneuploidy

CELL FREE FETAL DNAPOSITIVE PREDICTIVE VALUE

Age Age-related risk PPV

20 1 in 804 79%

30 1 in 526 86%

40 1 in 57 98%

Risk for Down syndrome

All drawn at 12 weeks

NT WITH CELL FREE FETAL DNA TEST

• Even if conventional analytes not used, there can be a benefit

• Increased NT >3.0mm or >99th centile OR cystic hygroma

• Genetic syndromes

• Isolated anomalies

• Heart

• Abdominal wall

• Diaphragmatic hernia

DIAGNOSTIC PROCEDURESChorionic villus sampling

Amniocentesis

CVS Amniocentesis

Timing 10-13 weeks >15 weeks

Complications if too early Limb reduction defects Clubbed foot, culture failure

Pregnancy loss 1 in 400 1 in 400

Same complication rate Transabdominal vs

transvaginal

Transplacental or not

KARYOTYPE

• Metaphase analysis of cultured cells

• Results in 7-14 days

• Detects >99% of aneuploides

MICROARRAY

• Whole genome SNP-based copy number microarray

• >2.5 million genomic sites

• Cultured or uncultured cells

• Can be used on nonviable cells

• Fetal death/stillbirth

DIAGNOSTIC GENETIC TESTS

Karyotype Microarray

Aneuploidy X X

Triploidy X

Small deletions/duplications X

Large deletions/duplications X X

Translocations/Inversions X X

Balanced rearrangements X

Low level mosaicism

Uniparental disomy X

Homozygocity X

DIAGNOSTIC TEST CHOICE

• Abnormal ultrasound and normal karyotype

• 6% have abnormal microarray

• Normal ultrasound and normal karyotype

• 1.7% have copy number variant (+/- pathogenic)

• Test choice

• General

• Anomalies characteristic of particular aneuploidy

• Abnormal screening or cell-free DNA testing

FISH-FLUORESCENT IN SITU HYBRIDIZATION

• Fluorescent-labeled probes for specific chromosome regions

• Uncultured cells-results about 2 days

• Common panels• Chromosomal 13/18/21/X/Y

• 22q11.2 deletion syndrome

• Screening test

• False + and false- possible

INVASIVE PROCEDURESWITH MATERNAL INFECTION

Hepatitis B - limited data

Vertical transmission dependent on viral load

Hepatitis B e antigen higher risk

Hepatitis C - limited data

Risk appears to be low

HIV - limited data

CART treatment/undetectable viral load=?transmission risk

ULTRASOUNDSecond trimester

ULTRASOUND FOR DETECTION OF ABNORMALITIES

• Major fetal anomaly detection: 84%

• Down syndrome detection: 50-60%

2014 NICHD Workshop for Fetal Imaging

CHROMOSOMAL MARKERSSECOND TRIMESTER

• Thickened nuchal fold

• Mild ventriculomegaly

• Echogenic intracardiac focus

• Pyelectasis

• Echogenic bowel

• Short femur length

CHROMOSOMAL MARKERSTHICKENED NUCHAL FOLD

• ≥6mm from outer edge of occipital bone to outer skin in midline

• Likelihood ratio 10-20 Down syndrome

• Detailed ultrasound

• Offer aneuploidy testing

CHROMOSOMAL MARKERSMILD VENTRICULOMEGALY

Lateral ventricular atrial measurement 10-15mm

Likelihood ratio 25 for Down syndrome

Detailed ultrasound

Aneuploid testing

Cytomegalovirus testing

Repeat ultrasound 3rd trimester

CHROMOSOMAL MARKERSECHOGENIC INTRACARDIAC FOCUS

• Incidence

Euploid 4%

Down syndrome 15-30%

Likelihood ratio 1.5 for Down syndrome

Isolated-offer aneuploidy screening

If screening negative, no further evaluation is required

CHROMOSOMAL MARKERSPYELECTASIS

• Renal pelvis ≥4 mm in AP diameter up to 20 weeks gestation

• Likelihood ratio 1.5 for Down syndrome

• Isolated-offer aneuploidy screening

• Repeat ultrasound 3rd trimester

CHROMOSOMAL MARKERSECHOGENIC BOWEL

• Fetal small bowel as echogenic as bone

• Likelihood ratio 6 for Down syndrome

• Aneuploidy, intra-amniotic bleeding, cystic fibrosis, cytomegalovirus

• Aneuploidy screening or diagnostic testing

• CF testing and CMV testing

CHROMOSOMAL MARKERSSHORT FEMUR LENGTH

• Measure <2.5% for gestational age

• Observed/expected femur length ≤0.91

• Likelihood ratio 2.0 Down syndrome

Aneuploidy, fetal growth restriction, skeletal dysplasia

Detailed ultrasound and counseling

Repeat ultrasound in 3rd trimester

SECOND TRIMESTER ULTRASOUND

• Limits of 2nd ultrasound markers

• Lack of standardization in measurements

• Confounding factors

• High maternal BMI

• Multiple gestation

• Machine quality

• Experience of ultrasonographer

MULTIFETAL GESTATION

• Decreased effectiveness of screening

• # fetuses and zygosity

• How does a single aneuploid fetus affect management?

MULTIFETAL GESTATION

• NT screen only-9% false positive • 75% detection

• Absent nasal bone • Found in 69% Down syndrome

• Up to 2.6% of euploid fetus

• Detection by zygocity-5% false positive rate• 73% monozygotic

• 43% dizygotic

• Cell free fetal DNA – limited data

CONCLUSION

Right test

Right time

Right patient

ONE SIZE DOES NOT FIT ALL