Prenatal Testing And
Screening
Lecture Outline
1.
Definitions
2.
Age related risks
3.
Etiology and phenotype of chromosome anomalies
4.
Risks, phenotype and testing options of ONTD
5.
1st and 2nd Trimester Prenatal Testing Options
6.
1st and 2nd Trimester MS Screening Options
7.
New approaches to combining these tools
8.
Ultrasound as a screening tool
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.
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
• Sensitivity=True positives/all affected
• Specificity=True negatives/all unaffected
Baseline Risk for Having a Child With a
Serious Birth Defect
3-5%
WE DON’T GET BETTER WITH AGE
Maternal
Age
20
30
33
34
35
36
37
38
39
40
41
DS Risk
Birth
All Chrom Abn
Birth
DS risk Mid
trimester
1/185
1/592
1/465
1/384
1/285
1/243
1/385
1/287
1/225
1/177
1/178
1/149
1/123
1/105
1/139
1/109
1/80
1/63
1/1231
1/685
1/452
1/352
1/274
1/213
1/166
1/129
1/100
1/80
1/85
1/48
1/61
NORMAL MALE KARYOTYPE 46,XY
NORMAL FEMALE KARYOTYPE 46, XX
WHEN MEIOSIS FAILS
Nondisjunction
Normal
Sex cell
production
Sex Cells
Sex Cells
Monosomy
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
~1/700
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
Trisomy 18, Edward syndrome
1/8000
Facial
Central Nervous System
Trisomy
18
•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
short dorsiflexed big toes
fixed flexion deformity of the fingers
(overlapping of the 2nd and 5th fingers over
the 3rd and 4th fingers)
simple arch pattern of the fingers and toes
hypoplasia of fingernails
single crease of 5th finger or all fingers
severe mental retardation
hypotonia -> hypertonia
neural tube defects
poor suck and weak cry
failure to thrive
ocular anomalies
Respiratory
•apnea
Cardiovascular( >95%)
•major: VSD, ASD, PDA
•minor: transposition, ToF, coarctation, anomal
coronary artery, dextrocardia,
•aberrant subclavian artery, arteriosclerosis, P
bicuspid aortic and/or pulmonic valves
Gastrointestinal
•inguinal, umbilical, and/or
diaphragmatic hernia
•congenital defects:
•diastasis recti, heterotopic pancreas, malrota
Meckel's, tracheoesophageal fistula
Genitourinary
•cryptorchidism
•congenital defects:
double ureter, ectopic kidney,
horseshoe kidney, hydronephrosis,
polycystic kidney
47,XXY
•severe mental retardation
•coloboma,
•(a cleft palate) and/or a cleft lip
•hypotonia
•skeletal abnormalities (polydactyly)
•Renal
• T13 Patau syndrome
heart defects
• 1/5,000
•holoprocencephaly
1/1000
Kleinfelter syndrome
45, X
45, X
Miscarriage
Turner syndrome
1/3000 liveborns
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
Open Neural Tube Defects
Open lesions
Closed lesions
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.
INDICATIONS FOR PRENATAL DIAGNOSIS
 Maternal age > 35 years at EDC
 Abnormal maternal serum screening for:
DS cut off > 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)
PRENATAL DIAGNOSTIC PROCEDURES
 AMNIOCENTESIS
 CHORIONIC VILLUS SAMPLING
 PERCUTANEOUS UMBILICAL CORD SAMPLING
AMNIOCENTESIS
PERFORMED ROUTINELY 16-20 WEEKS
ULTRASOUND GUIDED
AMNIOCENTESIS
Amniocentesis Testing
• Chromosome analysis
• AF-AFP levels
• Acetylcholinesterase
ONTD
• Risk of miscarriage associated with
procedure 1/100-1/400
Advantages
•
•
•
•
Highly reliable results 99+%
Familiar
Long standing reputation
NTD detection
Disadvantages
• Late in gestation
– Decision making
– Privacy
– Mom feels movement
• Fear of needles
• Needle invades the sac
Fetus: 12 weeks gestation
Chorionic Villus
Sampling
Performed
>10 wks-13 weeks
Transcervical
Chromosome analysis
Risk 1/100-1/200
Transabdominal
• trophoblastic shell cells
• Syncitiotrophoblasts – poly-proliferate
tissue type=directs
• cytotrophoblasts
• Mesodermal core=tissue culture
• frorm finger-like extensions
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 test=risk of sampling a fetus potentially destined to miscarry
•
No ONTD testing
•
More risk of vaginal bleeding
•
Speculum
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
Fetal Blood Sampling
“PUBS”
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.
Reproductive Decision Making
RISK
Fetal Aneuploidy
Procedure
Related
RISK
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…………..
SECOND TRIMESTER
MATERNAL ANALYTES FOR ANEUPLOID
SCREENING
FETAL
Alpha-fetoprotein- AFP
Estriol- uE3
PLACENTAL
Estriol- uE3
Human chorionic gonadotrophin- hCG
Inhibin-A
nd
2
Trimester MSS Overview
Used for detection of:
1.
2.
3.
4.
ONTD
Down syndrome
trisomy 18
Smith-Lemli-Opitz syndrome
Second trimester
MSS
ONTD
Serum Marker
AFP
DS X
MoM
0.7
HCG
uE3
Inhibin-A
2.1*
T18
SLO
0.65
0.36
0.21*
0.7
2.1
0.4*
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 < 0.4 MoM
• ~2% baby affected
• Testing AF for 7-8- dehydrocholesterol (7/8-DHC) levels
Other……..
Turner
Serum Marker
AFP
HCG
uE3
Inhibin-A
T13
Triploidy
Pregnancy complications
uE3 lower than 0.1 MoM
• Increase risk for x-linked ichthyosis
ONTD screening
• Abnormal Screen MS-AFP > 2.5 MoM
• Elevated MSAFP recommendations:
– Ultrasound
– 90% r/o spinal lesions
100% r/o anencephaly
– VWD reduced with normal scan
– If MSAFP >4.0 MoM and NL U/S
offer invasive testing
Detection Rates
MSAFP
• Anencephaly
• Spina Bifida
100%
85-90%
• VWD
– Omphalocele 70%
– Gastroschisis 90%
Add Ultrasound
100%
90%
95%
95%
2nd
Screening for DS
Trimester 1/270 Cut-off
DR%
FPR%
• Age
20
5
• Age AFP
30
5
• Age AFP + HCG
(Double)
• Age AFP+uE3+HCG
(Triple)
• Age AFP+uE3+HCG+Inhibin-A
(Quad)
55
5
61
7
75
5
The detection rate for Down syndrome
using the second trimester triple
screen is:
50% for women <35 y/o
88% for women >35 y/o
and
~60% for all women
Quad ~75%
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
~90% trisomy 18
1/270
1/100
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
First Trimester Screening
DS
T18
• Free beta HCG
• PAPP-A
• NT
>3.0 mm
Down syndrome DR ~1:270 Cut-off
FPR
MA + NT1
10%
DR
71%
MA + Biochemistry3
67%
MA + NT +
Biochemistry2
>80%
5%
1. Schuchter et al. Prenatal Diagnosis 22: 211, 2002
2. Wapner et al. NEJM 349: 1405, 2003
3. Spencer et al UOG 1999
Nasal bone
Recommendations 1st Trimester
Nuchal >3.5
• CVS
• Targeted ultrasound evaluation 18-20
• Echocardiogram
• Residual 5-6% risk neonate may have
a yet undefined genetic syndrome…
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
Integrated Screening
Timeline weeks
10-14
DR: 94-96%
FPR: 5%
16-19
18-20
PAPP-A and Nuchal
+
Quad Screen
=
Results
Screen Positive
1/270 DS
1/100 T18
2.5> ONTD
US
Amnio
Nothing
Screen Negative
Decision Making
20+ wks
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
Contingent
First Trimester Screening
High risk
Offer CVS
Low Risk
Intermediate
Triple Screening Integration
Low Risk
Stop
High risk
US and Amnio
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
RISK OF ANEUPLOIDY BASED ON GA AND
ANOMALY
3D Ultrasound
Fetal Face
24 weeks Gestation
Fetal MRI
FETOSCOPY
Umbilical cord
Amnion (stuck twin)
QUESTIONS ??