Amniocentesis and CVS

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Amniocentesis and CVS

• Dr. Joseph Har-Toov
• Lis Maternity Hospital
• Tel-Aviv, Israel

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Methods of chromosomal evaluation

• Non invasive
• Fetal cells from maternal blood
• preimplantation embryos (PGD)
• Invasive
• amniotic fluid (amniocentesis)
• placenta (chorionic villus tissue)
• Fetal blood

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Invasive techniques

• Amniocentesis
• Late second trimester after 15 weeks
• Early earlier than 15 weeks
• Chorionic villus sampling (CVS)
• Abdominal
• Trans cervical
• Trans vaginal
• Fetal blood sampling

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karyotype
fish
PCR
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What can be evaluated?

• Chromosomal aberrations
• Trisomy,
• Monosomy,
• Polyploidy,
• Marker chromosome,
• Deletion, duplication, inversion, translocation,
  ring chromosome .
• Genetic aberrations (DNA)
• Infectious disease
• Biochemical markers (AFP)

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Amniocentesis

• First introduced by Serr and Fuchs and Riis in
  the 1950s for fetal sex determination
• Only at the late 70th a static ultrasound was
  used to locate the placenta and amniotic fluid
  pocket
• Only In 1983, Jeanty reported a technique of
  amniocentesis under ultrasound vision

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Mid Trimester Amniocentesis

• Per coetaneous
• 20-23g needle
• Ultrasound guided
• Usually 20cc amniotic fluid
• Results 2 to 3 weeks

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complications

• Pregnancy loss 0.3-1.0.
• Increase risk
• Needle larger than 18g
• Multiple needle insertion
• Discoloration of the fluid
• High AFP, multiple late abortions, previous
  vaginal bleeding
• Placental perforation recent studies didnt
  find correlation

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Complications

• Leakage of amniotic fluid (better prognosis than
  spontaneous leakage)
• Amnionitis
• Vaginal bleeding
• Needle puncture of the fetus
• Long term complications
• Respiratory distress??
• Isoimmunization??

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Amniocentesis and HIV positive women

• Increased rate of vertical transmission
• Chemoprophylaxis previous to amniocentesis
  appears to be beneficial in preventing vertical
  transmission

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Multiple Gestation

• Three methods
• Indigo carmine injection to the first sac
• A single needle puncture sampling technique
  (Jeanty 1990)
• Simultaneous visualization of two needles on each
  side of the separating membrane (Bahado-Singh
  1992)
• Abortion risk probably higher
• Detailed description of fetus
  position and placental location
  

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Early Amniocentesis 9-14 weeks

• Introduced at late 80th
• 10-14 weeks gestation
• Only the amniotic (inner) sac should be aspirated
• Approximately 1 cc for gestational age
• Higher rate of pregnancy loss, talipes
  equinovarus, and post procedural amniotic fluid
  leakage
• laboratory failure op to 20

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Chorionic villus sampling

• Was developed in the 80th
• percutaneous transabdominal with 19-20g needle

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Chorionic villus sampling

• Was developed in the 80th
• percutaneous transabdominal
• transvaginal
• transcervical

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• 15-30mg each aspiration
• 20mg ideal for cytogenetic testing
• 30-40mg for cytogenetic and other direct
  molecular and biochemical tests

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CVS results

• Direct analysis examines the trophoblast cells of
  the placenta (very rapidly dividing cells)
• Results in few hours
• greater vulnerability to mitotic error
• Cultured analysis examines the fibroblast like
  cells of the villus stroma or mesenchymal core.
• Approximately 7-10 days
• Accurately reflect the chromosomes of the fetus. 

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Risk of invasive procedure

• Early amniocentesis
• High pregnancy loss
• High fetal malformations
• High rate of multiple needle insertions (4.7)
• High rate laboratory failures (1.8)
• Late amniocentesis
• Low pregnancy loss (0.3-1)
• Low rate of multiple needle insertions (1.7)
• Low rate laboratory failures (0.2)

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Risk of invasive procedure - CVS

• Transabdominal CVS as safe as second trimester
  amniocentesis
• Trans abdominal and transcervical CVS are equally
  safe and efficacious, provided that centers have
  expertise with both approaches
• In approximately 35 of cases, clinical
  circumstances will support one approach over the
  other
• Limb reduction not after 9 weeks

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mosaicism

• True chromosomal mosaicism is when two or more
  abnormal cells lines are detected in two or more
  culture flasks from the same individual.
• Pseudomosaicism is a term used to describe two
  abnormal cell lines that are found in only one
  culture flask (not reported to the patient)

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mosaicism

• Most often involving trisomic cell and normal
  cells
• 1-2 of pregnancies undergoing CVS
• 0.1 of pregnancies undergoing amniocentesis
• Clinical outcome of chromosomal mosaicism is
  strongly dependent on the specific chromosome
  involved and the number of trisomic cells in both
  the placenta and the fetus

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Mosaicism (trisomic cells) in CVS

• Option of an additional prenatal diagnostic
  procedure (amniocentesis or fetal blood sampling)
  

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Mosaicism (trisomic cells) in CVS

• Four possible conditions
• Mosaicism only in the placenta not affecting the
  fetus or placental function.
• Mosaicism only in the placenta not affecting the
  fetus but alter placental function (IUGR)
• Trisomy cells are both in the placenta and in the
  fetus
• Trisomy cells in the placenta and uniparental
  disomy in the fetus

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Mosaicism (trisomic cells) in amniotic fluid

• Probably there are trisomic cells in the fetus
• The true level and distribution of trisomic cells
  cannot be accurately assessed with any prenatal
  procedure
• Ultrasound is often the best judge of how a baby
  is developing

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Uniparental Disomy

• Arises when an individual inherits two copies of
  a chromosome pair from one parent and no copy
  from the other parent
• Maternal UPD two copies from the mother
• Paternal UPD two copies from the father

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How does UPD happen?

• Loss of a chromosome from a trisomic zygote,
  "trisomic rescue"
• Duplication of a chromosome from a monosomic
  zygote, "monosomic rescue"
• Fertilization of a gamete with two copies of a
  chromosome by a gamete with no copies of the same
  chromosome, called gamete complementation.

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Trisomic rescue following an error in meiosis
heterodisomy
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Trisomic rescue followed an error in meiosis II
isodisomy
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UPD - health concerns in people for two possible
reasons

• Parental imprinting in the case of heterodisomy
  and isodisomy
• Unmasking of recessive conditions in some cases
  of isodisomy

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Clinical consequences of UPD

• molecular UPD testing should be considered for
  certain chromosomes (including 6, 7, 11, 14, 15)
  that are known to have adverse phenotypic
  imprinting effects. 

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Factors considered when trying to predict the
outcome of mosaicism

• the chromosome involved
• A mosaic finding 18 or 21 is likely to have worse
  implications
• mosaic finding for trisomy 15 or 16 is likely to
  have less implications (trisomy 15 or 16 cells
  cannot survive )

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Factors considered when trying to predict the
outcome of mosaicism

• The tissues affected and level of trisomy in
  those tissues
• The tissue affected cannot be evaluated
• The level of trisomy can be only estimated   

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Factors considered when trying to predict the
outcome of mosaicism

• method of ascertainment  
• CVS shows that the placenta is affected
• Amniotic fluid suggests that at least one fetal
  tissue may be affected
• Fetal blood sampling confirms the diagnosis of
  chromosomal mosaicism

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Factors considered when trying to predict the
outcome of mosaicism

• ultrasound findings  
• presence/absence of uniparental disomy  
• number of previous case reports known in the
  literature  

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Thank you