Concept of Screening
Population (pregnant women)
Screening test
Screen Positive
Diagnostic test
• Amniocentesis
• CVS
• Fetal blood sampling
Screen Negative
No further test
Prenatal Screening
 Structural abnormalities
 Chromosome abnormalities
Chromosome abnormalities
 Trisomy 21
 Trisomy 13
 Trisomy 18
 Monosomy X
 Triploidy
Chromosome abnormalities
Prenatal diagnosis

Chorionic villous sampling

Amniocentesis

Fetal blood sampling

Preimplantation genetic diagnosis
But ! All methods subject to risk of miscarriage
Screening for Down syndrome
 Maternal age
 Ultrasonography
 Maternal blood tests
 Combined
Incidence of Down syndrome
Maternal age
LB
2nd trim.
25 years
1/1250
1/887
30 years
1/965
1/685
35 years
1/386
1/274
38 years
1/182
1/129
40 years
1/100
1/78
45 years
1/31
1/22
Maternal age for DS screening
Age group
Pregnancy
DS baby
Age > = 35 yr.
10 %
20-30 %
Age > 35 yr.
90 %
70-80 %
Women < 35 years
low risk
70-80% of Down syndrome
Neglected
Ultrasonography
First trimester screening
 Nuchal translucency (NT)
 Nasal bone
Observations on an ethnic classification of idiots
Langdon Down
“ ….. The nose is small. The
skin has a slight dirty
yellowish tinge, and is
different in elasticity, giving
the appearance of being too
large for the body.”
Nuchal Translucency (NT)
Nuchal translucency (NT)
Measurement of NT
Nuchal translucency (NT)
Measurement of NT
Measurement of nuchal translucency
The maximum thickness of the
subcutaneous translucency between
the skin and the soft tissue overlying
the cervical spine should be measured
by placing the callipers on the lines as
shown. During the scan, more than one
measurement must be taken and the
maximum one should be recorded.
+
+
+
+
+
+
+
+
+
+
Measurement of (NT)
 CRL 45-84 mm
 GA 11-13 wk
 Fetus
- Sagittal section
- Neutral position
- Occupies 3/4 of image
Reference range of fetal nuchal translucency with CRL
showing the 5th, 25th, 50th, 75th and 95th centiles
The 11-14-week scan. The diagnosis of fetal abnormalities
Likelihood ratios for trisomy 21 in relation to the
deviation in fetal nuchal translucency thickness
The 11-14-week scan. The diagnosis of fetal abnormalities
Recent studies examining the implementation of
fetal nuchal translucency screening at 10-14 weeks
Authors
Risk cutoff
DR(%)
96,127
1 in 300
82.2
8.3
3,550
1 in 300
91.0
4.9
11,398
1 in 300
76.0
4.7
4,523
1 in 300
83.0
4.7
Gasiorek-Wiens et al
23,805
1 in 300
87.6
13.0
Zoppi et al
12,495
1 in 300
90.0
9.0
Brizot et al
2,996
1 in 300
90.0
7.4
Snijders et al
Theodoropoulos et al
Adekunle et al
Schwarzler et al
N
DR = Detection rate ; FPR = False positive rate
FPR(%)
Observations on an ethnic classification of idiots
Langdon Down
“ ….. The nose is small. The
skin has a slight dirty
yellowish tinge, and is
different in elasticity, giving
the appearance of being too
large for the body.”
Absence of nasal bone in fetuses with
trisomy 21 at 11-14 weeks of gestation
Cicero S, et al. The Lancet 2001
Estimated sensitivity and false positive rate for risk
cutoffs in screening for trisomy 21
Risk
cutoff
NT screening
Sensitivity (%)
NT and NB screening
FPR (%)
Sensitivity (%)
FPR (%)
1 in 20
57.36
0.98
81.90
0.62
1 in 35
62.88
1.35
85.89
1.02
1 in 50
65.03
1.76
86.81
1.30
1 in 100
72.09
3.01
88.65
1.64
1 in 150
74.54
4.32
89.26
1.98
1 in 200
77.30
5.71
90.18
2.37
1 in 250
80.67
7.08
91.41
2.68
1 in 300
82.21
8.28
92.02
3.02
1 in 500
85.58
14.00
92.94
4.37
1 in 1000
92.33
27.40
94.7
8.15
Cicero S, et al. The Lancet 2001
Nuchal translucency in twin pregnancies
Sebire NJ,e t al. Br J Obstet Gynaecol 1996
• 448 twin pregnancies
• Fetal nuchal translucency thickness was measured
by ultrasound examination at 10-14 weeks
• Sensitivity and false positive rates of screening for
trisomy 21 were calculated
• The sensitivity is similar to that in singleton
pregnancies
• The specificity is lower because translucency is
also increased in chromosomally normal
monochorionic twin pregnancies
Fetal karyotyping in twins
In twin pregnancies, selection of the
appropriate invasive technique depends on the:
• Accuracy of obtaining a result from both fetuses
• Procedure-related risk of fetal loss
• The risks of selective fetocide should the
pregnancy be found to be discordant for an
abnormality and the parents choose this option
Fetal karyotyping in twins
There is an additional advantage of
screening by measurement of nuchal
translucency thickness; when there is
discordancy for a chromosomal
abnormality, the presence of a
sonographically detectable marker
(increased nuchal translucency) helps to
ensure the correct identification of the
abnormal twin should the parents choose
selective termination.
3-D ultrasound measurement of fetal nuchal translucency
• It can be used to replicated nuchal
translucency measurements only when
nuchal skin can also be clearly seen on
2-D ultrasound.
Paul C, et al. Ultrasound Obstet Gynecol 2001
• The possibility of rotating a stored
volume and inspecting it in three
orthogonal planes makes 3-D ultrasound
a useful tool for nuchal translucency
measurements, especially in doubtful
cases.
Clementschitsch G, et al. Ultrasound Obstet Gynecol 2001
Conditions associated with
increased nuchal translucency
 Cardiac defects
 Body stalk anomaly
 Diaphragmatic hernia
 Campomelic dysplasia
 Exomphalos
 EEC syndrome
 Achondrogenesis type II
 Fetal akinesia-
 Achondroplasia
 deformation sequence
 Asphyxiating thoracic dystrophy
 Fryn syndrome
 Beckwith-Wiedemann syndrome
 GM1-gangliosidosis
 Blomstrand
 Hydrolethalus syndrome
 osteochondrodysplasia
Genetic Sonogram:
Ultrasound indicators for Down
1. Structural anomalies
: Cardiac anomaly, DU atresia
2. Soft marker
: Echogenic intracardiac foci
Pyelectasis, Femur length Humerus Length
Structural anomalies
Trisomy 13
90%
Trisomy 18
70-80%
Trisomy 21
20%
Soft ultrasound makers
 Nuchal skin fold thickness
 Choroid plexus cyst (CPC)
 Mild ventriculomegaly
 Nasal bone
 Echogenic intracardiac foci (EIF)
 Echogenic bowel
 Renal pyelectasia
 Hypoplastic middle phalanx of the fifth digit
Nuchal skin fold thickness
Langdon Down (1866)
=  thickness of skin of the back
Benacerraf et al (1985)
= Using as an U/S marker for Down
Fig NT
Cut off threshold of nuchal thickness
 > 6 mm.
 16-20 wks gestation
 Down abnormal nuchal thickness 40%
 LR: 17 (CI 8-35) => Expert review is recommended,
and karyotyping should be offered
 Sensitivity 34%
 Specificity 99.5%
Nuchal thickness : Efficacy
Associated with
- Congenital heart disease
- Genetic syndromes (rare)
=> Expert review is recommended
Choroid plexus cyst (CPC)
 Cyst > 3 mm
 14 to 24 weeks’ gestation
 Locate in lateral ventricle
 Related more to Trisomy 18
 Not associated with other
fetal abnormalities or
abnormal postnatal
development.
CPC and Trisomy 18
 Snijders et al (1994)
Trisomy 18 (58 cases) CPC 50%
Normal fetusesCPC 1%
 Isolated CPCminimal increase risk
Isolated CPC
Trisomy 18
LR (trisomy 18) = 7 (CI 4-12)
Trisomy 21
Likelyhood ratio = 1.87 (CI 0.78-4.46)
Size, Disappearance and Laterality
=> not increase or reduce risk
Gross et al 1995, Gupta et al 1997 , Yoder et al 1999
Recommendation
• Fetal karyotyping should only be offered if isolated
CPCs are found in women 35 years or older or if the
maternal serum screen is positive for either trisomy 18
or 21
• All women with fetal CPCs and additional malformation
should be offered referral and karyotyping
• All women with CPCs and additional soft markers
should be offered additional counselling and further
ultrasound review
Mild ventricular dilatation
 Lateral ventricle : constant along gestation
 6.1 + 1.3 mm.
 Male : female = 6.4 :5.8 mm
 Definition 10-15 mm.
 Dangling choroid plexus > 3 mm.from medial wall
Isolate mild ventriculomegaly
 abnormal fetal karyotype ~ 3.8% (0-28.6%)
 0.15% of chromosomally-normal fetuses
 1.4% of trisomy 21 fetuses in the second trimester
 LR 9
Recommendations
• Neonatal assessment and follow-up are important to rule out
associated abnormalities and are important because of the
potential for subsequent abnormal neurodevelopment
• Cerebral ventricles greater than or equal to 10 mm are
associated with chromosomal and central nervous system
pathology. Expert review should be initiated to obtain the
following:
– a detailed anatomic evaluation looking for additional malformations
or soft markers
– laboratory investigation for the presence of congenital infection or
fetal aneuploidy
– MRI as a potential additional imaging technique
Echogenic intracardiac focus (EIF)
 A bright focus in papillary muscle
 Attach to cordae tendinae
 Move with valvar movement
 Calcium deposit and surrounded
by fibrous tissue
 Bettelheim et al 1999
- Lt ventricle 96%
- Both ventricle 4.3%
- Rt ventricle 4.7%
Fig
Bromley 1998
EIF
: Rt ventricle
: Both ventricle
Twice the risk
Wax + Philput 1998
EIF
: Multiple
: Dense echo
Increase risk
Location of EIF
 The evidence is best for left or biventricular EICF
 LR 2.8 (95% CI 1.5-5.5) =>high-risk women.
 Low-risk => LR 0–1.8
 Consensus of the SOGC Imaging and Genetics
Committees suggests an LR of 2
Recommendations
• EICF should be evaluated as part of the 4-chamber cardiac
review during the 16- to 20- week ultrasound
• Isolated EICF with a fetal aneuploidy risk less than 1/600 by
maternal age (31 years) or maternal serum screen requires no
further investigations
• Women with an isolated EICF and a fetal aneuploidy risk greater
than 1/600 by maternal age (31 years) or maternal serum
screening should be offered counselling regarding fetal
karyotyping
• Women with right-sided, biventricular, multiple, particularly
conspicuous, or nonisolated EICF should be offered referral for
expert review and possible karyotyping
Echogenic bowel
 echogenicity of abdominal content
 Compare to liver and bone echo
 Associated with
- Trisomy 21
- Congenital infection
- Meconeum ileus (cystic fibrosis)
- Bowel atresia
- FGR, FDIU
Echogenic bowel
Nyberg et al : Grading system
Grade 1 : mild echogenic ; diffuse
Grade 2 : mod echogenic ; focal
Grade 3 : Very echogenic ; bone echo
Echogenic bowel
 0.6-2.4% of all 2nd trimester fetuses
 Increased risk for fetal aneuploidy =>LR 6 (CI 2.7 - 6.8)
 Sensitivity 14.7%
 Specificity 98%
• Echogenic bowel seem to increase risk
• The more the echo, The higher the risk
Deren et al 1998
Recommendations
1. Evaluation of the fetal bowel should be done routinely
during 16-20 week obstetric ultrasound.
2. Echogenic bowel should be identified by comparison with
the echogenicity of surrounding bone using an
appropriate transducer and gain setting. Bowel
echogenicity equal to or greater than bone is significant
(grade 2 or 3).
3. No further investigation are required for grade 1
echogenic bowel
4. Grade 2 and 3 echogenic bowel is associated with both
chromosomal and nonchromosomal abnormalities.
Expert review is recommended to initiate the following:
a. detailed ultrasound evaluation looking for additional structural
anomalies or other soft markers of aneuploidy
b. detailed evaluation of the fetal abdomen looking for signs of bowel
obstruction or perforation
c. detailed evaluation of placental characteristics (echogenicity,
thickness, position, and placental cord insertion site)
d. genetic counselling
e. laboratory investigations that should be offered, including fetal
karyotype, maternal serum screening, DNA testing for cystic fibrosis
(if appropriate), and testing for congenital infection
MILD PYELECTASIS
5 mm - 10 mm
MILD PYELECTASIS
• Isolated pyelectasis 0.7%
• Isolated finding in fetal
Down syndrome ~ 2%
• LR for Down syndrome ~
1.9 (95% CI 0.7–5.1)
Recommendations
1. Evaluation of fetal kidneys is a part of the screening ultrasound at 16
to 20 weeks,’ and if pyelectasis is visualized, the renal pelvis should
be measured in the anterior/posterior diameter
2. All fetuses with renal pelvic measurements > 5 mm should have a
neonatal ultrasound, and those having measurements > 10 mm
should be considered for a third trimester scan
3. Isolated mild pyelectasis does not require fetal karyotyping
4. Referral for pyelectasis should be considered with additional
ultrasound findings and (or) in women at increased risk for fetal
aneuploidy owing to maternal age or maternal serum screen results
SHORT FEMUR LENGTH
Below 2.5th percentile or
Less than 0.9 of that predicted
by the measured BPD
- Sensitivity 16%
- FPR 4%
- LR 2.7 (95% CI 2.1-6.0)
SHORT HUMERUS LENGTH
Below 2.5th percentile or
Less than 0.9 of that predicted by the measured BPD
• Sensitivity 9%
• FPR 3%
• LR 7.5 (95% CI 4.5-12)
FIFTH FINGER CLINODACTYLY
•
•
•
3.4% of normal fetuses
18.8% of fetuses with
Down syndrome.
LR 5.6 (95% CI 2.5–11.9).
RISK ASSESSMENT
The Scoring Index
 Major anomaly
2
 Nuchal fold > 6 mm
2
 Short femur
1
 Short humerus
1
 Pyelectasis > 4 mm
1
 Hyperechoic bowels
1
 Echogenic intracardiac focus 1
J Ultrasound Med 11:449-458, 1992
Modified scoring index
Maternal age 35-39
1
Maternal age > 40
2
Scoring index > 2
Sensitivity 86.8%; False positive rate 27.1%
Abnormal genetic sonogram
one or more abnormal USG markers
- sensitivity
87%
- specificity
91%
- positive predictive values
11%
- negative predictive values
99.8%
Yeo L, Vintzileos AM: The use of genetic sonography to reduce the need for amniocentesis in
women at high risk for Down syndrome. Semin Perinatol 27:152-159, 2003
Likelihood Ratios for Down
Major anomaly
25.0
Nuchal fold
18.6
Hyperechoic bowels
5.5
Short humerus
2.5
Short femur
2.2
Echogenic intracardiac focus
2.0
Pyelectasis
1.6
No markers
0.4
Ultrasound Obstet Gynecol 1998;12:8-14.
The Extended Genetic Sonogram
Screening Modalities
 Maternal age
 Ultrasonography
 Biochemical markers
 Combined screening
Maternal age + free bhCG +
PAPP-A
Detection rate for Down 60%
“Combined testing”
Nuchal translucency and free bhCG and PAPP-A
Studty
Trisomy 21
GA
FPR(%)
DR(%)
Brizot et al 1994/1995
80
10-14
5.0
89
Orlandi et al 1997
11
10-14
5.0
87
de Graaf et al 1999
37
10-14
5.0
85
De Biasio et al 1999
13
10-14
3.3
85
Spencer et al 2000
210
10-14
5.0
89
Second Trimester
Biochemical Screening
 Triple Screening
- Alpha-fetoprotein
- Human chorionic gonadotropin
- Unconjugated estriol
 Other markers
- Dimeric inhibin A
- Dried blood, urine markers
Objective :
To increase prenatal detection of
 Down syndrome (DS)
 Neural tube defects (NTD)
 Trisomy 18
Timing ONLY between 14-21 weeks
AFP
Trisomy 21
Open NTD
Trisomy 18
hCG
uE3
Factors affecting triple analytes levels
 Gestational age
 Maternal weight
 Ethnicity
 Multiple pregnancy
 Smoking
 Type I diabetes mellitus
Screen positive for NTD
(AFP > 2.5 MoM)
 USG
- Confirm GA
- R/O twins, gross anomalies
 Repeat AFP test
 Targeted USG
- Brain (Lemon and Banana signs)
- Spine
Screen positive for DS
(DS risk) > 1:270
 USG
- Confirm GA
- R/O twins, gross anomalies
 Genetic counselling
- risk of DS based on age and TS results
- risk of amniocentesis (1:200)
Screen positive for trisomy 18
(Trisomy 18 risk > 1:100)
 USG
- Confirm GA
- R/O gross anomalies
 Genetic counselling
- risk based on age and TS results
- risk of amniocentesis (1:200)
Triple screen Negative
 DS screening efficacy
- 70% for women under 35 years
- 90% for women 35 years and over
 Open NTD Screening efficacy
- 95% for anencephaly
- 80% for spinal bifida
Second trimester
US screening vs Biochemical screening
• Sensitivity
• False positive
comparable
• Biochemical
– Reduce risk : more
– No need for highly skilled physician
• Combine test : most benefit
Diagnostic tests (Gold
standard)
 Karyotyping
- Down syndrome
- Trisomy 18
 Targeted ultrasonography
- Open neural tube defects
Prenatal diagnosis
Prenatal diagnosis has been called
“one of the most powerful advances
in medical technology.”
Amniocentesis
Technique
• Blindly
• Static ultrasound (late 1970s and early 1980s)
• Real-time ultrasound
- Marking
- Ultrasound guidance
Amniocentesis
Technique
• 16-20 weeks’ gestation
• 20-22 guage spinal needle
• Approximately 20 ml of amniotic fluid
is collected
• The first 1-2 ml of amniotic fluid is
discarded to minimise the chances of
maternal cell contamination
Amniocentesis
Safety
• The Canadian Collaboration Trial
– 1020 pregnancies
– No difference in loss rates from that of
controls
– Correlation between fetal losses and > 2
insertions per procedures and the needles of
19-guage or higher
CVS
Technique
• 9-12 weeks’ gestation
• Transcervical or transabdominal
(Equally safe and efficacious )
• The chorion frondosum, which contains
the most mitotically active cells, is the
area of the placenta that is sampled
Fetal blood sampling
Technique
1. Cordocentesis or Percutaneous
umbilical blood sampling (PUBS)
2. Intrahepatic vein sampling
3. Cardiocentesis
* 2 & 3 are associated with increased risks
PUBS
Technique
• 20-22 guage needle.
• The most commonly used location is
within 2 cm. of the placental insertion.
• Fetal blood have been obtained from
umbilical artery, but generally the
umbilical vein is preferred because it is
larger and less likely to be associated
with a fetal bradycardia.
Diagnostic embryofetoscopy
History
•Embryoscopy was first performed via the
transcervical approach early in gestation, previous
to fusion of the chorion and amnion, to make a
phenotypic diagnosis.
• Percutaneous techniques were then developed to
introduce the fetoscope directly into the amniotic
cavity transabdominally.
7 weeks’ gestation
14 weeks’ gestation
16 weeks’ gestation
Recommendation
Offer amniocentesis or CVS to
- Women age 35 years and over at EDC
- Previous aneuploidy
Offer screening to
- Women age 34 years or under at EDC
- Women age 35 years and over who are reluctant to
accept amniocentesis