Handbook of Genetic Counseling/Advanced Maternal Age - Chorionic Villus Sampling (CVS)-3

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Advanced Maternal Age - Chorionic Villus Sampling

Contracting[edit | edit source]

  • Introductions and small talk
  • Confirm referring obstetrician
  • Assess understanding for the referral
  • Elicit concerns and questions
  • As maternal age increases, we know that the risk for having a child born with a chromosome abnormality also increases.
  • The reason that we like to see women who are 35 or older is because we can offer testing options
  • I would like to start today by gathering some medical and family history information so that we can look for any other risk factors that we may need to talk about.
    • We want to see if there is anything in your history that could pose a risk to this pregnancy

Medical/Family History[edit | edit source]

  • LMP:_________
  • EDC:_________
  • Today's gestational age:_________
  • How has this pregnancy been going?
  • Any complications?
  • Have you had an ultrasound?
    • Date ________
    • Findings:______________
  • Anyone in the family have:
    • Birth defects, SABs, SB, MR, LD, chronic illness, or early cancers?
  • Tell them what I found; "looks good, it sounds like the pregnancy is going well, I don't see anything that concerns me"*
  • Do you have any questions?

Explanations of Genes and Chromosomes[edit | edit source]

  • All pregnancies are at a 3-5% risk of having a baby born with a birth defect.
  • Women are born with all the eggs that we will ever have, unlike men who continuously make sperm from puberty throughout their lives.
  • Eggs are stopped in a stage of division until one is ovulated each month.
  • The older the egg, the more likely a division error might occur.
  • General
  • Karyotype
  • Nondysjunction
  • Brief natural history of chromosome abnormalities

Age Related Risks[edit | edit source]

  • Patient's age at delivery: _______
  • Risk for Down Syndrome: 1 in ________ ( %)
  • Risk for any chrom. Abnormality: 1 in ________ ( %)

Options[edit | edit source]

  • Level II Ultrasound:
    • High resolution ultrasound
    • Done at 20+ weeks by an experienced technician
      • Better to see more of the developing organs
    • U/S detection rate for DS is about 60% and for trisomy 18 ~90%
    • Look for:
      • Heart
      • Brain
      • Shape of the head
      • Intestinal problems
      • Kidneys
      • U/S helps make us suspicious but doesn't give us a yes or no answer.

CVS as an Option[edit | edit source]

  • Offered between 10-12 weeks
  • Procedure used to obtain a sample of the placenta from the womb of an expectant mother.
  • Genetic make-up of placental cells is essentially the same at the fetus since they both come from the same original cell created at conception
    • When baby is created, the egg splits into two parts: a part that forms the baby and a part that forms the placenta
  • Analysis can detect many genetic disorders/chromosome abnormalities with 98-99% accuracy
    • Cannot detect about 90% of birth defects or the severity of a condition

Explain Procedure[edit | edit source]

  • Transcervical CVS
    • Only performed from 10-12 weeks
    • Preferred method if the placenta is posterior and close to the cervix
    • Sterile speculum is inserted and the vagina and cervix are cleaned with betadeine
    • By U/S guidance, a thin catheter is guided into the placenta
    • A syringe is attached and gentle suction is applied to aspirate the villi
    • Large sample (whole villi) taken
    • Catheter is removed
    • NOT recommended for women with a retroverted uterus
  • Transabdominal CVS
    • Easiest to perform with anterior or fundal placenta
    • Abdomen is cleaned with betadeine
    • A local anesthetic is applied to the skin
    • By U/S guidance, a needle is guided through the abdominal wall and uterine wall into the placenta (avoid the amniotic sac)
    • A syringe is attached and gentle suction is applied by the syringe plunger
    • The needle is moved back and forth with re-direction through the placenta
    • Small sample (pieces of villi) taken
  • Procedure takes roughly 5-7 min, after prep time
  • The sample is examined under the microscope to confirm that fetal tissue has been obtained. (If maternal tissue is present- repeat test).
  • Following the procedure, the baby's heartbeat will be monitored by U/S
  • Sample is sent to the lab for results
  • Direct vs. Culture results:
    • Direct analysis: A preliminary answer
      • Analysis of outer cells which are spontaneously dividing
      • Increased rate of error
      • Results in 1-2 days
      • Few labs do this

Culture analysis[edit | edit source]

  • Analysis of cells from mesenchymal core
  • More accurate
  • Results in 7-14 days
  • Results differ in about 2% of cases
  • Results will be reported by ????

Risks of complications[edit | edit source]

  • Miscarriage: increased above the background by 1%
  • Transverse limb reduction defects
    • Results show that the risk for transverse defects after CVS is ~1 in 3000 (0.03%)
    • Results show the greatest defects when CVS was performed prior to 10 weeks (limbs are formed at 10 weeks)
    • How? Suspected that instrumentation interrupts the vascular supply
    • VUMC has not had any CVS patients who had pregnancies born with limb reductions defects as a result of the procedure.

Disadvantages[edit | edit source]

  • Risk of laboratory failure
  • Maternal cell contamination
  • Mosaicism
    • Presence of two or more cell lines that differ with respect to their chromosomal constitution
    • Although the placenta and fetus start out the same, once they diverge- there is a very small chance that the placental cells might have a change that is not changed in the fetal cells - confined placental mosaicism
  • Insufficient sample obtained
  • With any of these, follow up is required.
    • Additional testing

Amniocentesis[edit | edit source]

  • Also an option, performed from 15+ weeks
  • Transabdominal removal of amniotic fluid
  • ~ same accuracy, but risks are 1 in 200 for complications.
  • Tests for NTD's

Follow-up[edit | edit source]

  • How do you feel about having a CVS? Would you like a few minutes to discuss the option with your partner?
  • Re-iterate that most babies are born healthy
  • Will want to do an u/s at about 18-20 weeks- anatomy is big enough to be easily visualized. (looking for structural anomalies)
  • MSAFP blood test (to detect NTD's)
  • Elicit final questions and concerns.

Notes[edit | edit source]

The information in this outline was last updated in 2001.