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8/7/2019 Prenatal Diagnostic Procedures
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Prenatal DiagnosticProcedures
Ultrasound
Amniocentesis
Chorionic Villus Sampling
Percutaneous Umbilical Cord Blood Sampling
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Specificity & Sensitivity
USG for NTD 97% sensitive / 100% specific
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Ultrasound
Royal College of Obstetric & Gynecology
recommend a two-stage scan program for
screening:
at booking (11-14 weeks)
at around 20 weeks
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Neural Tube Defect
Most common form of major abnormalities
detected is NTDs.
NTD affecting the cranial vault anencephalyor encephalocele
NTD affecting the spinal cord spina bifida
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Neural Tube Defect
Anencephaly or encephaloceles detected @
1st Trimester Ultrasound with adequate
examination of cranial vault.
Spina Bifida detected @ 20-week anomaly
scan. Visualization of lemon shape of skull
and banana signs in the fetal brain (absent
of cerebellum)
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(Cranial ultrasound findings
associated with "open" spina
bifida and the Chiari II
malformation.Inward scalloping of the frontal
bones (arrows), also known as the
"lemon sign."
Small posterior fossa and banana-
shaped cerebellum ("banana
sign") (short arrow) and effaced
cisterna magna (long arrow).
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Myelomeningocele. (A) Sagittal ultrasound image demonstrates the break in the skin line
(arrow). (B) Transaxial ultrasound image shows the myelomeningocele sac (short arrow) and
divergent posterior ossification centers (long arrows).
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Sensitivity: >95% (Obstetric by Ten Teachers)
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Amniocentesis
Aspiration of amniotic fluid from amniotic sac
via a needle inserted through the maternal
abdomen.
Started in 1996 diagnosis of genetic disease
Later confirm NTD (raised AFP)
Usually perform between 15-16 weeks.
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Amniocentesis
Types
Early Amniocentesis (11-14 weeks)
Second Trimester Amniocentesis (15-16 weeks)
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Amniocentesis
Method
Aseptic technique
22-gauge needle inserted through maternalabdomen under USG guidance and
visualization of needle tip.
Aspirate 15-20ml of fluid Culture of cells 2-3 weeks before testing
performed.
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Amniocentesis
Indications
Fetal Karyotyping when there is increased risk ofaneuploidy;
a) Women positive serum screening for DS
b) Women of advance maternal age (>35)
c) USG detection of abnormality or soft marker
d) Parental balanced translocatione) Previous history of chromosomal
abnormalities.
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Amniocentesis
Indications (ACOG)
Women 35 years of age and over
Parents who have had a child with Down syndrome orother chromosome abnormality
Couples who are known carriers of a chromosomearrangement
Couples who have had a child with a malformation of thebrain or spinal cord (spina bifida or anencephaly)
Couples who have a family history of a genetic condition forwhich testing is available
Pregnancies that are considered at an increased risk forchromosome abnormalities based on screening test
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Amniocentesis
Testing Method
Culture & Banded Karyotype
Time : 2-3 weeks
FISH : Fluorescence In-Situ Hybridization
PCR : Polymerase Chain Reaction
Time : within 24-48 hours
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Amniocentesis
Benefits:
Chromosomal Abnormalities (DS, Edward,
Pataus, Turners or Klinefelters) Congenital infections (CMV & Toxoplasmosis)
Diagnosis of NTD by estimating AFP and
acetylcholinesterase
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Amniocentesis
Complications
Fetal loss (1%)
Cell culture failure necessitating furtherinvasive test
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Early Aminiocentesis
Between 11-14 weeks of gestation
If done before membrane fusion to uterine
wall, puncture of sac would be difficult
lessfluid withdrawn (1ml/POG)
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Early Amniocentesis
Disadvantages compared to Second Trimester
Amniocentesis:
higher rate of post-proceduralpregnancy loss
STA (0.7%) ETA (2.5%)* Canadian Early and Mid-trimester Amniocentesis Trial Group
Positional foot deformities( neonatal talipes)
More cell cultures failure
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Chorionic Villus Sampling and
Placental Biopsy
Sampling of Placental Tissue
Placental biopsy if done after 1st trimester
Can be done from week 10 of gestation Early diagnosis early termination
Method: Trans-abdominal or Trans-cervical
Probe: catheter, needle aspiration, biopsy forceps
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Chorionic Villus Sampling
Couple recommended by ACOG to take CVS:
Women 35 years of age and older
Parents who have had a child with Downsyndrome or other chromosome abnormality
Couples who are known carriers of a
chromosome rearrangement
Couples who have a family history of a genetic
condition for which testing is available
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Chorionic Villus Sampling
Contraindications (Relative)
Vaginal bleeding or spotting
Active genital tract infection Extreme uterine ante or retro-flexion
Body habitus precluding clear USG
visualization or uterine access
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Trans-Abdominal CVS
Technique
Aseptic technique
18-20 gauge inserted through maternalabdomen to placental site under direct USG
guidance.
Placental tissue aspirated Fine biopsy forceps can be used through an
outer guide needle.
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Trans-Cervical CVS
Technique
Ideal for posterior low-lying placenta
Aseptic technique
Cervix and vaginal visualize through speculum
Trans-abdominal USG performed to visualizecervical canal.
Needle catheter or biopsy forceps introducedthrough cervix towards abdomen.
Placental tissue aspirated
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Chorionic Villus Sampling
When to choose which one?
Placental site
Axis of uterus Operator experience
Complications of each method
Trans-cervical CVS associated with less discomfortbuthigher risk of infection andprocedure related loss.
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Chorionic Villus Sampling
Complications
Fetal loss (> amniocentesis)
Placental mosaicism If done early
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Percutaneous Umbilical Cord Blood
Sampling Cordocentesis
Performed primarily for:
1. assessment and treatment of confirmed red cell or
platelet allo-immunization2. analysis of non-immune hydrops
3. Genetic analysis when CVS and amniocentesis resultsare confusing
Can also be used for:1. Metabolic & hematological studies
2. Acid-base analysis
3. Viral cultures
4. Immunological studies
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Percutaneous Umbilical Cord Blood
Sampling
Method
16-18 weeks of gestation
20-gauge needle introduced through maternalabdomen under USG guidance
Aspiration from umbilical cord from placental
insertion or fetal insertion of umbilical cord
Avoid artery may cause vasospasm bradycardia
Cardiac puncture or intrahepatic vessels can also be
sampled.
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Percutaneous Umbilical Cord Blood
Sampling
Indications
Rapid high quality karyotyping (48-72H) if
abnormality detected late Fetal hematological problem (anemia or
thrombocytopenia)
Assess acid base status in IUGR
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Percutaneous Umbilical Cord Blood
Sampling
Complications
Bleeding at site of needle fetal bradycardia
Cord hematoma
Fetal maternal hemorrhage
Fetal loss (1-2%)
Introduction of infection
Transmission of HIV
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Laboratory Analysis
Cytogenic Analysis
Cells are cultured until enough cells in mitosis areavailable
Longer time
FISH
Detects and localized specific DNA sequences
directly in interphase or metaphase Rapid prenatal Dx of major aneuploidies for
Chromosome 13,18,21,XY
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Laboratory Analysis
DNAAnalysis
DNAprobe for sickle cell disease / cystic
fibrosis
PCR (fragile X syndrome, congenital toxo and
CMV)
Linkage analysis (fragile X syndrome)
Biochemical & enzymatic analysis
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Summary of Prenatal Diagnostic
ProcedureAmniocentesis Chorionic Villus
Sampling
Cordodentesis
Gestation 11-13 / >14 weeks 10-40 weeks 20-40 weeks
Route Trans-abdominal Trans-abdominal /
Trans-cervical
Trans-abdominal
Cells sampled Fetal fibroblast Trophoblast Fetal white blood
cells
Procedure related
risk of miscarriage
1% 1% 1%
Direct Karyotype
Result
FISH
24-48 hours
24-48 Hours Not needed
Culture karyotype
result
2-3 weeks 1-2 weeks 24-48 hours
Mosaicism rate of
karyotype
None 1% None
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References
1. Lennon, C.A. (1999) Sensitivity andSpecificity of Ultrasound
for the Detection of Neural Tube and Ventral Wall Defects
in a High-Risk Population,Obstetrics & Gynecology: Vol94 -
Issue 4 - p 562-566
2. Williams Obstetric22nd Edition (2005)
3. Obstetric and Gynaecology, An evidence-based text for
MRCOG (2004)
4. Obstetric by Ten Teachers 18th Edition (2006)
5. Guidelines of the Malaysian Medical Council