Screening of down syndrome during pregnancy

1. Prenatal Diagnosis of
foetal Down Syndrome
Latest approaches
1

2. Down syndrome
• Down syndrome can be caused by
one of three types of abnormal cell
division involving chromosome 21.
• The three genetic variations include:
1-Trisomy 21- More than 90 % of Down
syndrome cases are caused by
trisomy 21.
2

3. 3

4. 4

5. 5

6. Down syndrome
• An extra chromosome (chromosome 21)
originates in the development of either
the sperm or the egg.
• When the egg and the sperm unite to
form the fertilized egg, three (rather
than two) chromosomes 21 are present.
• As the cells divide the extra
chromosome is repeated in every cell. 6

7. Down syndrome
2-Mosaic Trisomy 21 – This is a rare form
(less than 2% of cases) of Down
syndrome. While similar to simple
trisomy 21, the difference is that the
extra chromosome 21 is present in
some, but not all cells, of the
individual.
This type of Down syndrome is caused by
abnormal cell division after fertilization.
7

8. Down syndrome
• The name comes from a random order
of normal and abnormal cells (a mosaic).
• In cellular mosaicism, the mixture can
be seen in different cells of the same
type;
• while with tissue mosaicism, one set of
cells may have normal chromosomes
and another type may have trisomy 21.
8

9. Down syndrome
3-Translocation Trisomy 21-
Sometimes (in 3-4% of cases)
part of chromosome 21 becomes
attached (translocated) to
another chromosome (usually
the 13th, 14th or 15th
chromosome) before or at
conception. 9

10. Down syndrome
• The carrier (the one having the
translocated chromosome) will
have 45 chromosomes instead
of 46 but they will have all the
genetic material of a person
with 46 chromosomes
10

11. Down syndrome
• This is because the extra chromosome 21
material is located on a different
chromosome (the translocated one).
• A carrier will have the extra material but
will have only one chromosome 21.
• The carrier will not exhibit any of the
symptoms of Down syndrome because
they have the correct amount of genetic
material.
11

12. Diagnosing Down Syndrome
• Since many expectant parents
choose to forgo prenatal tests,
most cases of Down syndrome are
diagnosed after the baby is born.
• Doctors will usually suspect Down
syndrome if certain physical
characteristics are present.
12

13. Diagnosing Down Syndrome
• Some of the Traits Common To Babies with Down
Syndrome Include
• Low muscle tone
• A flat facial profile
• A small nose
• An upward slant to the eyes
• A single deep crease across the center of the palm
• An excessive ability to extend the joints
• Small skin folds on the inner corner of the eyes
• Excessive space between large and second toe 13

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15. Diagnosing Down Syndrome
• Not all babies with Down syndrome
have all these characteristics, and
many of these features can be found,
to some extent, in individuals who do
not have the condition.
• Therefore, doctors must perform a
special test called a karyotype before
making a definitive diagnosis.
15

16. Diagnosing Down Syndrome
• To obtain a karyotype, doctors draw a
blood sample to examine your baby's
cells.
• They use special tools to photograph the
chromosomes and then group them by
size, number and shape.
• By examining the karyotype, they can
determine accurately whether or not
your baby has Down syndrome 16

17. TWO TYPES OF TEST FOR
DOWN'S SYNDROME
• Two types of procedures are
available to pregnant women:
• Screening tests and diagnostic tests
• Screening tests estimate the risk of
the baby having Down syndrome.
• Diagnostic tests tell whether or not
the baby actually has Down
syndrome 17

18. TWO TYPES OF TEST FOR
DOWN'S SYNDROME
Screening tests estimate the chances
of your baby having Down's
syndrome.
These tests are offered to pregnant
women regardless of age..
It is possible to have the tests carried
out privately, at a cost.
18

19. TWO TYPES OF TEST FOR
DOWN'S SYNDROME
• Diagnostic tests, such as CVS and
amniocentesis, give you a definite result.
• These may be offered if your screening
test shows you have a high risk of having
a baby with a chromosomal condition.
• Diagnostic tests do unfortunately carry a
slight risk of miscarriage, which is why
screening tests are used first.
19

20. Diagnostic Tests
• Three diagnostic tests are currently
available:
• Amniocentesis is performed between 12
and 20 weeks gestation.
• Chorionic Villus Sampling (CVS) is
conducted between 8 and 12 weeks.
• Percutaneous Umbilical Blood Sampling
(PUBS) is performed after 20 weeks.
20

21. DIAGNOSTIC TESTS
• These tests are “invasive” and require
sampling either the amniotic fluid or the
placenta with a needle.
• Although the risk is small, approximately 1 in
200 babies will be lost as a result of genetic
amniocentesis and 1 in 100 will be lost as a
result of CVS.
• Also, neither test can test for the majority of
birth defects associated with normal
chromosomes. 21

22. Amniocentesis
• This procedure is used to collect amniotic
fluid, the liquid that is in the womb. It's
performed in the doctor's office or in the
hospital on an "out-patient" basis.
• A needle is inserted through the
mother's abdominal wall into the
uterus, using ultrasound to guide the
needle.
22

23. Amniocentesis
• Approximately one ounce of fluid is
taken for testing.
• This fluid contains fetal cells that can
be examined for chromosome tests.
• It takes about 2 weeks to determine
if the fetus has Down syndrome or
not 23

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26. Amniocentesis
• Amniocentesis is usually carried out
between the 14th and 18th week of
pregnancy; some doctors may do
them as early as the 13th week.
• Side effects to the mother include
cramping, bleeding, infection and
leaking of amniotic fluid afterwards.
26

27. Amniocentesis
• There is a slight increase in the risk of
miscarriage: the normal rate of
miscarriage at this time of pregnancy is 2
to 3%, and amniocentesis increases that
risk by an additional 1/2 to 1%.
• Amniocentesis is not recommended
before the 14th week of pregnancy due
to a higher risk of complications and loss
of pregnancy. 27

28. Which mothers should have an
amniocentesis?
• The current recommendations by
professional obstetric groups is
that women with a risk of having
a child with Down syndrome of 1
in 250 or greater should be
offered amniocentesis.
28

29. Chorionic Villus Sampling (CVS)
• In this procedure, instead of amniotic fluid
being taken, a small amount of tissue is
taken from the young placenta (also called
the chorionic layer).
• These cells contain the fetal chromosomes
that can be tested for Down syndrome.
• The cells can be collected the same way as
the amniocentesis, but another method is to
insert a tube into the uterus through the
vagina.
29

30. 30

31. Chorionic Villus Sampling (CVS)
• The method depends on the mother's
anatomy.
• CVS is usually carried out between the 10th
and 12th weeks of pregnancy.
• Side effects to the mother are the same as
with amniocentesis (above).
• The risk of miscarriage after CVS is slightly
higher than with amniocentesis, increasing
the normal risk of miscarriage to 3 to 5%. 31

32. Procedure-related Risks
Amniocentesis
 Pregnancy loss
1:300-1:500
 Spotting or leakage
1-2%
 Needle injury - rare
 Infection - rare
CVS
 Pregnancy loss -
similar to
amniocentesis
 Spotting - up to 32%
 Leakage or infection
- less than 0.5%
32

33. PERCUTANEOUS UMBILICAL CORD BLOOD SAMPLING
• (PUBS), also called cordocentesis, is a
diagnostic genetic test that examines
blood from the fetal umbilical cord to
detect fetal abnormalities.
• PUBS provides a means of rapid
chromosome analysis and is useful when
information cannot be obtained through
amniocentesis, CVS, or ultrasound
33

34. PERCUTANEOUS UMBILICAL CORD BLOOD SAMPLING
• This test carries a significant risk of
complication and is typically reserved
for pregnancies determined to be at
high risk for genetic defect.
• PUBS is similar to amniocentesis, but
instead of sampling the amniotic fluid
which surrounds the fetus, PUBS
examines fetal blood. 34

35. PERCUTANEOUS UMBILICAL CORD BLOOD SAMPLING
• An advanced imaging ultrasound
determines the location for needle
insertion into the placenta, and the
needle is guided through the
mother's abdomen and uterine wall
into the fetal vein of the umbilical
cord, where a fetal blood sample is
removed. 35

36. PERCUTANEOUS UMBILICAL CORD BLOOD SAMPLING
• The sample can then be sent for
chromosomal analysis.
• The entire process lasts 45 minutes
to an hour.
• Because the fetal vein is fragile early
in pregnancy, PUBS is performed no
earlier than 17 weeks into
pregnancy. 36

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38. Screening tests for Down’s syndrome
• Screening tests won't be able to tell
you for certain that your baby is or
isn't affected by Down's syndrome.
• Screening tests can help you to
decide whether or not to have a
diagnostic test, which will tell you
with greater certainty.
38

39. Down syndrome and trisomy 18 risk
assessments
• Prenatal screening is routinely offered for Down
syndrome and NTDs and is accompanied by a risk
assessment for trisomy 18.
• Screening for NTDs is based on alpha-
fetoprotein (AFP) alone whereas Down
syndrome and trisomy 18 risk assessments
are based on multiple marker combinations
that include maternal age and 2 or more of
the following:
39

40. Down syndrome and trisomy 18 risk
assessments
• pregnancy-associated plasma protein A
(PAPP-A),
• nuchal translucency (NT),
• AFP,
• human chorionic gonadotropin (hCG),
• unconjugated estriol (uE3), and
• dimeric inhibin A (DIA). 40

41. Screening Markers
41

42. PREGNANCY ASSOCIATED PLASMA
PROTEIN A
• Glycoprotein of unknown function
• Only reliable for detection of DS
between 10-13 weeks
• Levels are 60% lower in DS
• Highest detection rate of any
marker (42%)
42

43. Inhibin A test
• The inhibin A test is done to measure the
amount of this hormone in a pregnant
woman's blood to see if the baby may
have Down syndrome.
• Inhibin A is made by the placenta during
pregnancy.
• The level of inhibin A in the blood is used
in a maternal serum quadruple screening
test. 43

44. What is Inhibin A?
• alpha-beta subunit glycoprotein hormone
• inhibits the secretion of FSH from the anterior pituitary
• synthesized in ovary and placenta (Inhibin B is synthesized in
ovary and testis)
• molecular weight approx. 32,000 daltons
• inhibin-A = alpha subunit + betaA subunit
Pro-a subunit
bA subunit
bB subunit
Inhibin A
Inhibin B
44

45. Screening tests for Down’s syndrome
• Our Antenatal Screening Service
provides five screening tests for Down’s
syndrome. These are the
• Integrated test,
• the Serum Integrated test,
• the Combined test,
• the Quadruple test, and the
• Quadruple plus NT test. 45

46. integrated screening
•integrated screening – the
best method for detecting
Down syndrome in the
whole population
46

47. Full integrated test
• — The full integrated test
consists of NT and PAPP-A
measured at 10 to 13 weeks
followed by measurement of
AFP, uE3, hCG, and inhA at
15 to 18 weeks 47

48. Serum integrated test
•Clinical Use
•Prenatal screening for Down
syndrome and open neural
tube defects (NTDs)
•Identify pregnancies at high
risk for trisomy 18 48

49. Serum Integrated Screen
• The Serum Integrated Screen is the same
as the Integrated Screen, except NT
measurement is not used.
• Though the Serum Integrated Screen has
a lower detection rate than the
Integrated Screen, it is the test of choice
when an accurate NT measurement is
not available. 49

50. Serum integrated test
•The serum integrated test
combines a blood test for:
•PAPP-A and hCG before 14
weeks of pregnancy
•AFP, uE3 and inhibin A (INH)at
15 weeks to 20 weeks 50

51. The Serum Integrated test
• The serum integrated test is an option
for women who are unable to have a
nuchal translucency measurement
performed.
• The test is performed in two stages.
• The first stage is ideally carried out at 11
weeks of pregnancy (but any time
between 10 and 13 weeks is acceptable),
when a blood sample is obtained.
51

52. The Serum Integrated test
• The second stage involves a second
blood sample which is ideally taken at
15 or 16 weeks, but between 14 and
22 weeks is possible.
• The Serum Integrated test includes
screening for open neural tube
defects (spina bifida and
anencephaly). 52

53. The Combined test
• The Combined test only uses first trimester
markers, and is performed at around 11
weeks of pregnancy (but any time between
10 and 13 weeks is acceptable) when a blood
sample is obtained and an ultrasound
examination is carried out.
• The Combined test is not as effective as the
integrated test, but is suitable for women
who are prepared to accept a less effective
test in order to have an earlier result. 53

54. The Quadruple test
• The Quadruple test only uses second
trimester markers, and is performed at
around 15 or 16 weeks of pregnancy (but
between 14 and 22 weeks is possible)
when a blood sample is obtained.
• The test is suitable for women who
book after 13 weeks of pregnancy and
are too late for the Integrated test. 54

55. The Quadruple plus NT test
• The Quadruple plus NT test is an option for
women who have had a nuchal translucency
(NT) performed but wish to utilise the second
trimester serum markers to improve
screening performance.
• The NT measurement is incorporated into
the Quadruple test interpretation.
• The Quadruple plus NT test includes screening
for open neural tube defects (spina bifida
and anencephaly). 55

56. Five maternal serum analytes units
• For the five maternal serum analytes used in
Down syndrome screening, the units most
commonly used in the United States are:
• AFP — either ng/mL or IU/mL
• uE3 — ng/mL
• beta-hCG — mIU/mL or IU/mL
(tripple screen test)
• inhA — pg/mL
• PAPP-A — ng/mL or mIU/mL 56

57. Maternal Serum Screening for
Trisomy 21 and 18
Serum marker Trisomy 21 Trisomy 18
AFP
hCG
uE3
Inhibin-A N/A
57

58. Similarity of
hCG and inhA
distributions in
Down syndrome and
unaffected pregnancy
58

59. Sequential Screening for DS
Offer 1st trimester screen
(NT, PAPP-A, hCG)
DS risk >1 in 50
Offer counseling & CVS
DS risk <1 in 50
2nd trimester screen with
Integrated Result
(NT, PAPP-A,AFP, hCG, uE3,
Inhibin)
DS risk >1 in 270
Offer counseling & amnio
Uses both 1st and 2nd
trimester results to adjust
maternal age risk for DS
and takes advantage of
higher detection rate 59

60. Contingent testing
Contingent screening is defined in terms of three risk
cut-offs:
• (1) women at very high risk of having a fetus with
Down syndrome after first trimester combined
testing are offered immediate invasive prenatal
diagnosis,
• (2) women at very low risk are provided with their
risk estimate and require no additional testing, and
• (3) women at intermediate risk have second
trimester markers tested (AFP, uE3, hCG, and inhA)
to get an integrated result.
60

61. Contingent
First-trimester Screen
High Risk Intermediate Risk Low Risk
Offer CVS Quad Screen No Further Testing
Offer Amino if HR
61

62. NON-INVASIVE PRENATAL TESTING
(NIPT)
• NIPT, which analyzes cell-free
fetal DNA circulating in maternal
blood, is a new option in the
prenatal screening and testing
paradigm for trisomy 21 and a
few other fetal chromosomal
aneuploidies.
62

63. NON-INVASIVE PRENATAL TESTING
(NIPT)
• Quantitative differences in
chromosome fragments in
maternal blood can be used to
distinguish fetuses affected with
trisomy 21, and a few other fetal
aneuplodies, from those that are
not affected. 63

64. Non-Invasive Prenatal Testing
(NIPT)
• Testing can be done any time after 10 weeks;
typically it is done between 10-22 weeks.
Results can take a week or more.
• At least 99% of all pregnancies with trisomy
21 can be detected using this test.
• However, up to 1 in 100 pregnancies with
trisomy 21 will have a normal result and be
missed on screening.
64

65. NON-INVASIVE PRENATAL TESTING
(NIPT)
• The testing is non-invasive,
involving a maternal blood draw,
so the pregnancy is not put at risk
for miscarriage or other adverse
outcomes associated with invasive
testing procedures.
65

66. Non-Invasive Prenatal Testing (NIPT)
• The two most promising methods are
• NIPD using next generation
sequencing technologies and
• NIPD using Methylation DNA
Immunoprecipitation (MeDIP)
with real time qPCR.
66

67. Diagnosis after birth
• Once your baby is born, the initial
diagnosis of Down syndrome is
usually based on your baby’s physical
appearance.
• If your doctor needs to definitively
diagnose Down syndrome, they will
arrange for a blood test known as a
chromosomal karyotype. 67

68. Diagnosis after birth
• A sample of your baby’s blood will be
taken and sent to a laboratory so that the
chromosomes in the blood can be
analysed.
• If the blood test finds that there
is an extra chromosome 21, your
baby will be diagnosed with
Down syndrome. 68

69. THE AGA KHAN UNIVERSITY HOSPITAL
CLINICL LABORATORY
Stadium Road P.O. Box 3500, Karachi 74000, Pakistan
Tel # (92) (21) 493001 Extension # 1918/1931
DOWN’S SYNDROME & NEURAL TUBE DEFECT SCREENING
LAST NAME _________________________ FIRST NAME______________________
MR # / L# ___________________________ SAMPLE ID_______________________
PHYSICIAN_______________________________________________________________
DATE OF BIRTH (d/m/y) ________________ PHONE # _________________________
ETHNIC ORIGIN ______________________
CLINICAL DETAILS
MATERNAL WEIGHT (KGS) __________________
DIABETIC ____________________
IVF PREGNANCY__________________
PREVIOUS PREGNANCIES WITH DOWNS’s ____________________________________________
(Mention NONE or ONE or TWO or More Than TWO)
PREVIOUS PREGNANCIES WITH NTD’S ____________________________________________
(Mention NONE or ONE or TWO or More Than TWO)
ULTRASOUND SCAN
NUMBER OF FETUS _____________________________________________________________________
SCAN PERFORMED ON __________________________________________________________________
GESTATIONAL WEEKS (BY SCAN) ______________________ (+DAYS) _____________________________
DATE OF BLOOD SAMPLE TAKEN __________________________________________________________
RESIDENT NAME _____________________________
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