Chorionic villus sampling

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IN THE NAME OF GOD
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Chorionic villus sampling

• DR TABASSI

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INTRODUCTION 

• Chorionic villus sampling (CVS) refers to a
  procedure for the prenatal diagnosis of genetic
  disorders in which small samples of the placenta
  are obtained for chromosome or DNA analysis.
• A larger amount of DNA is derived from CVS than
  from cells obtained at amniocentesis.

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TECHNICAL CONSIDERATIONS 

• A transvaginal sonographic examination should
  precede the procedure to determine
• The number of embryos
• Chorionicity
• Fetal viability
• Major fetal structural anomalies.

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• Personnel 
• sonographer and the physician
• assistant with an on-site microscope can provide
  rapid evaluation of sample adequacy
• Technique
• Transcervical (TC)
• Transabdominal (TA).

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Transcervical chorionic villus sampling 

• Cervicovaginal cultures should be obtained prior
  to a transcervical procedure to identify any
  potential pathogens (gonorrhea, chlamydia, group
  B streptococcus), which we treat with appropriate
  antibiotics.

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Transcervical chorionic villus sampling

• Materials
• 26 cm long polyethylene cannula with outer
  diameter of 1.5 mm and a soft stainless steel
  blunt obturator
• Sterile speculum
• Metal sound
• 20-mL syringe containing nutrient medium
• Single-toothed tenaculum or ring forceps
  (optional).
• Biopsy forceps

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Transabdominal chorionic villus sampling 

• Materials
• Sterile pocket for the ultrasound probe and
  sterile gel
• 20 gauge needle, 9 or 12 cm long, with stylet
• 20 to 30 mL syringe containing nutrient medium
• Holder to mount the syringe, which makes
  aspiration easier

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Multiple gestations 

• Knowledge of the chorionicity of multiple
  gestations is essential prior to CVS, as
  chorionicity determines the number of samples to
  be taken

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INDICATIONS 

• CVS enables prenatal diagnosis of conditions in
  which diagnostic
• Cytogenetic or DNA analysis is possible.
• Rapid karyotyping can be achieved within 48 hours
  of sampling by examining cytotrophoblastic cells
  in metaphase
• Long-term cultures should be performed
  concurrently.

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• The most common indication for cytogenetic
  testing by CVS is an increased risk of fetal
  aneuploidies due to advanced maternal age, family
  history, or abnormal first trimester screening
  for Down syndrome.

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ALTERNATIVES

• Amniocentesis is an alternative to CVS as both
  procedures provide the same information
• Amniocentesis for prenatal diagnosis can be
  performed in the first trimester (ie, early
  amniocentesis, typically at 11 to 13 weeks of
  gestation but before 15 weeks)
• Early amniocentesis is not recommended for most
  women because it is associated with a higher rate
  of pregnancy loss and complications than either
  CVS or midtrimester procedures.

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CONTRAINDICATIONS

• Contraindications to TC-CVS include
• Vaginismus
• Cervical stenosis
• Cervical myomas
• Cervical infection
• Lower uterine segment myomas obstructing access
  to a fundal placenta
• Severe anteflexion or retroflexion of the uterus
  that renders the placenta inaccessible to the
  catheter despite uterine manipulation.

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CONTRAINDICATIONS

• Contraindications to TA-CVS rarely occur
• Extreme uterine retroflexion with intestinal
  loops between the abdominal wall and uterus
• Fetal position obstructing access to a posterior
  placenta

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CONTRAINDICATIONS

• Relative contraindications to either type of CVS
  include
• Maternal isoimmunization
• Presence of an intrauterine device.
• Risk factors for neural tube defects.

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TIMINING

• This procedure generally is performed at 10 to 13
  weeks

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COMPLICATIONS 

•  The most serious complications from CVS are
• fetal damage
• fetal loss
• bleeding
• infection
• uncertain results

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COMPLICATIONS 

• Total fetal loss
• CVS is less safe than second trimester
  amniocentesis, and the excess risk seems to be
  confined to TC CVS.
• TC CVS is associated with higher rates of
  spontaneous losses among euploid fetuses than TA
  CVS.

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COMPLICATIONS 

• Perinatal mortality rate
• The cumulative perinatal mortality rate is not
  significantly higher after CVS than amniocentesis
  independent from the type of CVS (TC or TA)

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COMPLICATIONS 

• Surviving children 
• Only one of the above trials described the
  rate of surviving children, which was 4.6 percent
  lower in women undergoing CVS compared to
  amniocentesis

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Predictors of fetal loss

• Small for gestational age fetuses have a higher
  loss rate after the procedure compared to
  normal-sized fetuses.
• The number of times the sampling device has to be
  introduced before obtaining adequate tissue
  affects the overall fetal loss rate .
• The operator's skill and experience play an
  important role in the rate of fetal loss

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Multiple gestation 

• These risks are not significantly different from
  those reported with CVS in singletons or with
  early second trimester amniocentesis in twins .
• The risk of a sampling error in twin gestation,
  though small (0.6 to 0.8 percent), is higher than
  that with amniocentesis and it seems to be even
  greater in triplets and higher order gestations
  (1.2 percent).

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Confined placental mosaicism 

• Thus, an abnormal karyotype found only in the
  trophoblastic cells usually represents confined
  placental mosaicism, with no effect on fetal
  phenotype.
• An abnormal karyotype in the mesenchymal
  cells is more likely to reflect a true abnormal
  fetal karyotype. Amniotic fluid cells, which
  originate from the epiblast of the inner cell
  mass from which the embryonic tissues arise,
  closely reflect the constitution of the embryo.
  Confined placental mosaicism, a term referred to
  any case of abnormality restricted to the
  placenta (trophoblast or mesenchyme), and not
  involving the fetus, is associated with greater
  risk of fetal growth restriction.

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COMPLICATIONS

• Limb-reduction defects and oromandibular
  hypogenesis
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• An increased rate of transverse limb
  abnormalities has been reported when CVS is
  performed at less than nine weeks of gestation
• This risk is independent of the expertise of the
  operator, the route of the procedure (TA versus
  TC), or gauge of the needle or cannula used
• Thus, 10 weeks is the generally accepted lower
  limit for CVS procedures
• The limb reduction is associated with
  oromandibular hypogenesis (called the
  oromandibular-limb hypogenesis syndrome

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Transverse digital defects associated with
chorionic villus sampling. 
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COMPLICATION

• Failure at obtaining sample
• The sampling success rate in the majority of the
  studies is at least 99 percent after fewer than
  three insertions it is not different for TC-
  versus TA-CVS  

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COMPLICTION

• Bleeding  
• Vaginal spotting after CVS is reported in up to
  one-third of women, but frank bleeding occurs in
  less than 6 percent and is more common after the
  TC- than TA- CVS.
• A subchorionic hematoma is detected by ultrasound
  following up to 4 percent of TC-CVS

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COMPLICATION

• Infection
• Chorioamnionitis (0 to 0.5 percent of cases)
  maternal septic shock (three cases)
• Maternal intestinal perforation (during TA-CVS)
  leading to peritonitis have been reported .
• Subclinical intrauterine infection is the cause
  of part of the excess fetal losses reported after
  TC-CVS compared to TA-CVS
• TC-CVS appears to carry a higher risk of
  infection than TA-CVS

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COMPLICATION 

• Fetomaternal hemorrhage
• Fetomaternal hemorrhage has been documented based
  upon an increase in maternal serum
  alpha-fetoprotein following CVS.
• TA-CVS is associated with a greater risk of FMH
  than TC-CVS.
• FMH has been proposed as one cause of fetal loss
  after CVS, particularly when MSAFP is very high
  or continues to rise after CVS

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Complications 

• Obstetric complications 
• Study was that the CVS group had more risk
  factors for hypertension (eg, significantly
  greater maternal age and body mass index than the
  controls). Larger studies are needed to allow
  controlling for confounders

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COMPLICATION

• Long-term outcome 
• No increase in fetal and infant mortality,
  prematurity, low birthweight, nonreassuring fetal
  status, or limb reduction defects was found in
  association with CVS.

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SUMMARY

• CVS is the procedure of choice for first
  trimester prenatal diagnosis of genetic
  disorders.
• Compared with amniocentesis, CVS is associated
  with a greater risk of sampling and technical
  failures.
• The safety and efficacy of CVS have been
  documented.
• TA-CVS is preferable to TC-CVS Procedure-induced
  limb defects are negligible when the procedure is
  performed after 10 weeks of gestation
• Rh(D) negative nonsensitized women should receive
  anti-D Rh immunoglobulin prophylaxis after the
  procedure
• Second trimester amniocentesis is associated with
  the lowest risk of pregnancy loss chorionic
  villus sampling is safer than early (ie, before
  15 weeks) amniocentesis.

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THANKS