genetic testing in pregnancy: what are the options…ncus.org/files/fall2016/isler.pdf · genetic...
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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