obgyn

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Prenatal Testing And Screening
March 22, 2007 Genetics Board Review Lecture
Adel D. Gilbert, MS, CGC Genetic Medicine
Education Coordinator Institute of Genetic
Medicine Johns Hopkins University
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Lecture Outline

• Definitions
• Age related risks
• Etiology and phenotype of chromosome anomalies
• Risks, phenotype and testing options of ONTD
• 1st and 2nd Trimester Prenatal Testing Options
• 1st and 2nd Trimester MS Screening Options
• New approaches to combining these tools
• Ultrasound as a screening tool

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Testing Defined

• A procedure that (in most cases) provides a
• definitive answer to the question that is being
• asked. Tests that have low false positives and
• negatives are considered diagnostic.
• In the case of prenatal testing there is a risk
  of
• miscarriage associated with all the currently
• available diagnostic invasive tests.

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Screening Defined

• Identify those at increased risk who are not be
  perceived to be at risk
• Does not dx definitively
• Follow-up options available for definitive
  information
• SensitivityTrue positives/all affected
• SpecificityTrue negatives/all unaffected

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• Baseline Risk for Having a Child With a
• Serious Birth Defect

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WE DONT GET BETTER WITH AGE
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Maternal Age DS RiskBirth All Chrom Abn Birth DS risk Midtrimester
20 1/1231
30 1/185 1/384 1/685
33 1/592 1/285 1/452
34 1/465 1/243 1/352
35 1/385 1/178 1/274
36 1/287 1/149 1/213
37 1/225 1/123 1/166
38 1/177 1/105 1/129
39 1/139 1/80 1/100
40 1/109 1/63 1/80
41 1/85 1/48 1/61
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NORMAL MALE KARYOTYPE 46,XY
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NORMAL FEMALE KARYOTYPE 46, XX
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Sex Cells
Sex Cells
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T21 Tid Bits

• 70 T21 due to an error in maternal meiosis I
• 20 maternal meiosis II
• 5 occur during spermatogenesis (meiosis II)
• 5 of trisomic 21 error in mitosis
• no advanced maternal age and there is no
  preference for which chromosome 21 is duplicated
  in the mitotic error
• most common chromosomal abnormalities in liveborn
  children

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1/700
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Phenotype

• Moderate mental retardation
• Characteristic facies
• upslanting palpebral fissures
• epicanthic folds,
• midface hypoplasia,
• macroglossia
• Congenital malformations
• heart (30-40), atrioventricular canal
• gastrointestinal tract, such as duodenal stenosis
  or atresia, imperforate anus, and Hirschsprung
  disease
• Leukemia (both ALL and AML) 10-20x
• acute megakaryocytic leukemia occurs 200 to 400
  times more frequently in the Down syndrome
• 90 have significant hearing loss, usually of the
  conductive type

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Trisomy 18, Edward syndrome 1/8000
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Trisomy 18

• Facial
• microcephaly with prominent occiput
• narrow bifrontal diameter
• short palpabral fissures
• low-set malformed ears
• cleft lip /- palate
• narrow palatal arch
• micrognathia
• Skeletal
• neck
• webbed
• chest
• short sternum
• widely spaced nipples
• hips
• small pelvis, congenital dislocation of the hips,
  limited hip abduction
• extremities
• phocomelia
• rockerbottom feet or equinovarus

• Central Nervous System
• severe mental retardation
• hypotonia -gt hypertonia
• neural tube defects
• poor suck and weak cry
• failure to thrive
• ocular anomalies
• Respiratory
• apnea
• Cardiovascular( gt95)
• major VSD, ASD, PDA
• minor transposition, ToF, coarctation, anomalous
  coronary artery, dextrocardia,
• aberrant subclavian artery, arteriosclerosis, PS,
  bicuspid aortic and/or pulmonic valves
• Gastrointestinal
• inguinal, umbilical, and/or diaphragmatic hernia
  
• congenital defects
• diastasis recti, heterotopic pancreas,
  malrotation, Meckel's, tracheoesophageal fistula
  
• Genitourinary
• cryptorchidism

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47,XXY
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• severe mental retardation
• coloboma,
• (a cleft palate) and/or a cleft lip
• hypotonia
• skeletal abnormalities (polydactyly)
• Renal heart defects
• holoprocencephaly

• T13 Patau syndrome
• 1/5,000

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1/1000
Kleinfelter syndrome
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45, X
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45, X Miscarriage
Turner syndrome1/3000 liveborns
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Neural Tube Defects

• Second most common major congenital defect
  (1-2/1000)
• Not a chromosome anomaly
• Routinely tested and screened for in pregnancy
• Failure neural tube to close at 28 days
  gestation
• 20 are closed lesions and difficult to detect
  prenatally

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Open Neural Tube Defects
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Open lesions
Closed lesions
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In 1976 the American College of Obstetrics and
Gynecology recommended prenatal diagnosis be
offered to all women 35 years of age and older
at delivery.
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• INDICATIONS FOR PRENATAL DIAGNOSIS
• Maternal age gt 35 years at EDC
• Abnormal maternal serum screening for
• DS cut off gt 1/270
• Increased risk Trisomy 18 or 13
  Smith-Lemli-Opitz syndrome
• ONTD
• Previous child with chromosomal abnormality or
• diagnosable genetic disorder
• Balanced translocation carrier
• Ultrasound anomaly (soft sign vs frank anomaly)

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• PRENATAL DIAGNOSTIC PROCEDURES
• AMNIOCENTESIS
• CHORIONIC VILLUS SAMPLING
• PERCUTANEOUS UMBILICAL CORD SAMPLING

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AMNIOCENTESIS
PERFORMED ROUTINELY 16-20 WEEKS
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ULTRASOUND GUIDED AMNIOCENTESIS
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Amniocentesis Testing

• Chromosome analysis
• AF-AFP levels
• Acetylcholinesterase
• Risk of miscarriage associated with procedure
  1/100-1/400

ONTD
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Advantages

• Highly reliable results 99
• Familiar
• Long standing reputation
• NTD detection

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Disadvantages

• Late in gestation
• Decision making
• Privacy
• Mom feels movement
• Fear of needles
• Needle invades the sac

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Fetus 12 weeks gestation
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Chorionic Villus Sampling
Transcervical
Performed gt10 wks-13 weeks Chromosome
analysis Risk 1/100-1/200
Transabdominal
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• trophoblastic shell cells
• Syncitiotrophoblasts poly-proliferate tissue
  typedirects
• cytotrophoblasts
• Mesodermal coretissue culture
• frorm finger-like extensions

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Disadvantages

• Placental mosaicism 1 of CVS is confirmed in the
  fetus 10-40
• Second trimester amniocentesis mosaicism
  0.1-0.3 confirmed in a fetus up to 70 of the
  time.
• ?LRD risk prior to 70 days gestation (10 weeks)
• Higher loss rate
• Less access to procedure
• Higher chance of insufficient sample
• Early testrisk of sampling a fetus potentially
  destined to miscarry
• No ONTD testing
• More risk of vaginal bleeding
• Speculum

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Benefits

1. Earlier in gestation
2. rapidly growing cell cultures practically free of
   maternal cell contamination
3. an efficient direct method to obtain high quality
   metaphases from the of the syncitiotrophoblasts
   tissue which the fetal karyotype is defined
   within a few hours of chorionic villi sampling
   (specialty cyto techinque)
4. is suitable for a rapid, direct diagnosis of the
   related metabolic diseases.
5. placental mosaicism (trisomic rescue in fetus)
   can increase the risks of genetic abnormalities
   such as uniparental disomy

G. Simoni1, Human Genetics 1983  
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Fetal Blood Sampling PUBS
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Percutaneous Umbilical Cord Sampling(PUBS)or
Cordocentesis

• 2 risk of loss
• Technically difficult prior to 20 weeks
• Blood disorders such as hemophilia and anemia
• Useful for detection of Rh isoimmunization of the
  fetus (blood cell count and oxygen
  level)?erythroblastosis fetalis (HDN)
• Chromosomal abnormalities Fetal karyotype in 48
  hours
• Infections such as toxoplasmosis and rubella.
• The procedure is also used to perform blood
  transfusions to the fetus and to administer
  medication directly into the fetal blood supply.

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Reproductive Decision Making
RISK Fetal Aneuploidy
Procedure Related RISK
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TO TEST OR NOT TO TEST

• I want to know
• The benefits outweigh the risks
• Options are desirable
• Because my doctor says so..

• Not sure I want to know
• Risks are a big worry
• Options stink
• Because my doctor says so.

So what to do what to do..
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SECOND TRIMESTER MATERNAL ANALYTES FOR
ANEUPLOID SCREENING
FETAL Alpha-fetoprotein- AFP Estriol-
uE3 PLACENTAL Estriol- uE3 Human
chorionic gonadotrophin- hCG Inhibin-A
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2nd Trimester MSS Overview

• Used for detection of
• ONTD
• Down syndrome
• trisomy 18
• Smith-Lemli-Opitz syndrome

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Second trimester MSS
ONTD DS T18 SLO
AFP HCG uE3 Inhibin-A
0.65 0.36 0.4
Serum Marker
0.21
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Smith Lemli Opitz Syndrome

• Defect enzyme in the conversion of
  7-dehydrocholesterol to cholesterol.
• Affects 1 in 20,000 to 40,000 births
• Autosomal Recessive
• Mental Retardation
• Slow growth
• Heart defects
• Facial cleft
• Screen positive women have uE3 lt 0.4 MoM
• 2 baby affected
• Testing AF for 7-8- dehydrocholesterol (7/8-DHC)
  levels

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Other..
Turner T13 Triploidy Pregnancy
complications
AFP HCG uE3 Inhibin-A
Serum Marker
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uE3 lower than 0.1 MoM

• Increase risk for x-linked ichthyosis

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ONTD screening

• Abnormal Screen MS-AFP gt 2.5 MoM
• Elevated MSAFP recommendations
• Ultrasound
• 90 r/o spinal lesions
• 100 r/o anencephaly
• VWD reduced with normal scan
• If MSAFP gt4.0 MoM and NL U/S
• offer invasive testing

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Detection Rates
MSAFP
Add Ultrasound

• Anencephaly 100 100
• Spina Bifida 85-90 90
• VWD
• Omphalocele 70 95
• Gastroschisis 90 95

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Screening for DS 2nd Trimester 1/270 Cut-off
DR
FPR

• Age 20 5
• Age AFP 30 5
  
• Age AFP HCG 55 5 (Double)
• Age AFPuE3HCG 61 7 (Triple)
• Age AFPuE3HCGInhibin-A 75 5 (Quad)

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• The detection rate for Down syndrome
• using the second trimester triple
• screen is
• 50 for women lt35 y/o
• 88 for women gt35 y/o
• and
• 60 for all women Quad 75

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First Trimester Integrated Screening For
Trisomies FIRST

• Entire analysis performed 11-13 6/7 weeks
  gestation
• MS free Beta hCG and PAPP-A (pregnancy associated
  plasma protein)
• -obtained bw 9-13 weeks
• Nuchal measurement 11-13 6/7
• Maternal age
• Detection Rates
• 80 Down syndrome 1/270
• 90 trisomy 18 1/100

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Nuchal Translucency (NT)

• Gestation 11 to 13 6/7 wks
• Mid-sagittal view
• Fetus away from amnion
• Enlarge head upper thorax
• Widest part of NT

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First Trimester Screening
DS
T18

• Free beta HCG
• PAPP-A
• NT

gt3.0 mm
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Down syndrome DR 1270 Cut-off
DR
FPR
MA NT1 10 71
MA Biochemistry3 67
MA NT Biochemistry2 5 gt80
1. Schuchter et al. Prenatal Diagnosis 22 211,
2002
2. Wapner et al. NEJM 349 1405, 2003
3. Spencer et al UOG 1999
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Nasal bone
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Recommendations 1st Trimester Nuchal gt3.5

• CVS
• Targeted ultrasound evaluation 18-20
• Echocardiogram
• Residual 5-6 risk neonate may have a yet
  undefined genetic syndrome

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Fetal Nasal Bone

• 65 DS have absent nasal bone
• General population 1
• African Americans 8-10
• Secondary screen
• Difficult to obtain
• Higher false positive in 1st

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Integrated Screening
Timeline weeks
PAPP-A and Nuchal
10-14

16-19
Quad Screen
DR 94-96 FPR 5

18-20
Results
Screen Positive 1/270 DS 1/100 T18 2.5gt ONTD
Screen Negative
Decision Making20 wks
US
Nothing
Amnio
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Advantages

• Increases detection rate
• Decreases false positive rate (fewer tests and
  fewer procedure related losses)
• Disadvantages
• Long wait time for result
• Unable to utilize CVS and early detection
• Late GA by the time amnio results final

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Contingent
First Trimester Screening
High risk
Low Risk
Intermediate
Triple Screening Integration
Offer CVS
High risk
Low Risk
US and Amnio
Stop
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Advantages

• Increase detection rate 90
• Decrease FPR 2
• Reduce the number of amnios performed in low risk
  pregnancies

Disadvantages

• New (limited data)
• Hard to determine uptake
• Offered at few institutions

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RISK OF ANEUPLOIDY BASED ON GA AND ANOMALY
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3D Ultrasound Fetal Face 24 weeks Gestation
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Fetal MRI
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FETOSCOPY
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Umbilical cord
Amnion (stuck twin)
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QUESTIONS ??