prenatal diagnostic procedures

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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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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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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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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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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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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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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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

prenatal diagnostic procedures

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