IN THE NAME OF GOD
Prenatal screening
E . ZAREAN
Fellowship of perinatology
Congenital Disorder
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Genetic
Chromosomal
Enviromental
Infection
Morphogenesis defect
Baseline Risk for Having a Child With a
Serious Birth Defect
3-5%
First and Second Trimester
Screening
Prenatal Testing
Screening versus Diagnosis
First trimester versus Second trimester
Serum and/or Ultrasound
Low-risk versus High-risk Women
Diagnostic versus Screening
(-)
(+)
No overlap:
Positive test is abnormal
Overlap:
Positive test could be
normal or abnormal
Is Prenatal Testing for
Everyone?
consult
• An explanation of the difference between a
screening test and a diagnostic test.
• Screening sensitivity and specificity
compared to diagnostic testing.
• Description of the performance of various
screening tests .
• The risks associated with prenatal diagnosis
• The psychological implications of prenatal
screening and diagnosis .
• The implications of having a child with
Down syndrome .
• The detection rate of chromosomal
abnormalities other than Down syndrome,
and the implications of having a child with
one of these abnormalities .
• Information about the length of time
necessary to obtain results from screening
and diagnostic testing .
• Information about pregnancy termination .
Screening Performance:
The challenge in screening is to have a test that has a high
detection rate and low false positive rate.
Detection Rate :
(sensitivity)
percentage of affecteds called
screen positive by the test
The higher the better!
False Positive Rate :
(1 – specificity)
percentage of unaffecteds called
screen positive by the test
The lower the better!
First trimester Screening
Nuchal translucency
Free beta HCG
PAPP-A
Combined NT and Serum
Nuchal Translucency (NT)
Amnion
Skin
First Trimester US – Nasal Bone
Nasal bone present in a euploid
fetus in the first trimester
Nasal bone absent in a fetus with
T21in the first trimester
Nuchal Translucency
(NT)
Measurement
“normal nuchal translucency” “increased nuchal translucency”
Second trimester screening
• AFP
• B-HCG
• Unconjucated estriol
• Inhibin A
Contingent
First-trimester
Screen
High Risk
Intermediate
Risk
Low Risk
Offer CVS
Quad Screen
No Further
Testing
Offer Amino
if HR
Positive screen test
• Most parents are anxious because they do
not fully understand that most positive
results are associated with a normal
pregnancy outcome.
• after than negative diagnostic test some
anxiety related to the false-positive
screening test may persist .
• On the other hand, normal results may have
psychological benefits for the reassured
parents.
• Consult : DR – FPR – Advantage –
Disadvantage
• Multiple pregnancy
Case 1
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Age 27
8 weeks pregnant
G2P1
Previous pregnancy uncomplicated
Married for 5 years, healthy 3 year old
daughter
Case 1
• What prenatal genetic screening options
would you discuss with her?
– Discuss options with benefits, limitations,
availability.
– New screening tests may require earlier first
prenatal visit .
Case 1
• If she was 38…..?
– Could go directly to CVS, amnio
– Combined /Integrated test more accurate than age .
• What might affect her decision?
• Miscarriage rate .
• Performance of amnio/CVS compared to sequential test.
– May detect problems other than Down syndrome .
• Her perception of risk/morbidity associated with Down
syndrome.
• Her personal/family/religious beliefs…
Case 2
• Age 34
• 17 weeks pregnant
• To discuss result of integrated screen.
Case 2
• Results:
Screening result
: *** SCREEN POSITIVE***
Reason
: Increased Risk of Down syndrome
Down syndrome risk
: 1 in 130 (at term)
Risk of NTD
: 1 in 7000
Comment
: Down syndrome risk due to maternal
age alone is 1 in 400
COMMENTS AND RECOMMENDATIONS
Down syndrome: The risk of Down syndrome is GREATER than the screening
cut-off of 1 in 250 at term. If the gestational age is confirmed, counselling
regarding the risks and benefits of AMNIOCENTESIS is suggested.
Case 3
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33 years old
G2P0
Miscarriage last year
Trying to get pregnant for several years
14 weeks pregnant
Following U/S for NT . you received report
from radiologist indicating NT is elevated
(4.0mm) for this gestational age
• What would be important to discuss with
Case 3
• she was referred for genetic counselling
– Offered:
• Chromosome testing
• Ultrasound 18 - 20 wks & echocardiogram 20 - 22
wks
– Counselled risk of miscarriage with CVS or
amniocentesis.
• May be even more significant for this couple in
view of infertility and miscarriage
High AFP
• Over than 2 MOM :
twin pregnancy
incorrect GA
ovarian tumor
hepatocellular tumor
IUFD
low birth weight
Placenta abruptio
Anomaly
open NTD
omphalocele ( 4 MOM )
gastroschisis (10 MOM )
teratoma
cystic hygroma
benign obstructive uropathy
fetal edema
skin defect
ultrasonography
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The sensitivity, specificity, and positive and
negative predictive values of ultrasound
evaluation for the detection of NTDs were 98,
100, 100, and 99.9 percent, respectively .
prenatal diagnostic procedure for fetal
karyotype, rather than serum screening
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A previous pregnancy complicated by fetal
trisomy .
At least one major or two minor fetal structural
anomalies in the current pregnancy .
Chromosomal translocation, inversion, or
aneuploidy in themselves or their partner .
Future Directions
First trimester US alone
3D/4D US
Noninvasive Isolation of fetal DNA
‫دستورالعمل کشوری‬
‫مشاوره بايد در اولين مالقات بارداري (هفته ‪ 6‬تا ‪10‬‬
‫بارداري) انجام شود‪.‬‬
‫درحال حاضر غربالگري جنين در سه ماهه اول بارداري‬
‫توصيه مي شود‪ .‬چنانچه خانم باردار پس از ‪ 13‬هفته و ‪6‬‬
‫روز و قبل از هفته ‪ 17‬بارداري مراجعه نمايد و غربالگري‬
‫سه ماهه اول را انجام نداده است‪ ،‬پس از مشاوره و انتخاب‬
‫والدين‪ ،‬غربالگري سه ماهه دوم بارداري درخواست مي شود‪.‬‬
QUESTIONS ??