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Genetic counseling: Chorionic Villus Sampling (CVS)

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Chorionic Villus Sampling (CVS)

IntroductionEdit

  • Discuss the reason for referral.
  • Elicit prior knowledge about CVS.
  • Elicit knowledge about AMA or other indications for session.
  • Assess concerns and set goals for the session.
  • Provide overview of topics for counseling session.

Client & Partner InformationEdit

  • Discuss why it's important to get pregnancy, personal, and family history.
  • Go over pregnancy history:
    • G?P?
    • LMP? EDC?
    • Infertility?
    • Exposures?
    • Medical complications?
    • How has the pregnancy been going?
  • Personal background:
    • Occupation?
    • Religion?
    • Ethnicity?
    • Chronic illness?
    • Partner exposure?

Elicit Family HistoryEdit

  • Construct pedigree:
    • Abnormal # miscarriages, stillbirths, infant deaths?
    • Previous children with chromosome abnormality, NTD, Down syndrome, birth defects, mental retardation?
    • Consanguinity?
    • Other concerns/risk factors?

What is AMA?Edit

  • Woman is age 35 & above at expected date of delivery.
  • As maternal age increases, risks of birth defects increase.
  • Women do not make new eggs like males make sperm.
  • They are born will all the eggs they will have in their life and these eggs mature with age.
  • There are procedures that can be done to assess the risk, but there are also risks associated with the procedures.
  • The age of 35 is the "magic" number because this is when the risk of the procedure is justified.
  • The background risk for major birth defects for women of all ages is 3-5%.

Explain Chromosome AbnormalitiesEdit

  • Explain cells, chromosome, and DNA
  • Show karyotypes
  • Explain nondisjunction
  • Show abnormal karyotypes (trisomy 13, 18, 21, sex chromosome anomalies)
  • Give a general description of the clinical features and prognoses.
    • Trisomy 18 & 13 are most severe with most affected dying before the age of 1 year
    • Trisomy 21 is more mild; characteristic physical features and mild to moderate MR
    • Turner and Kleinfelter's syndromes are sex chromosome anomalies. Also usually mild.

Quote RisksEdit

  • Show charts to figure risk of chromosome abnormalities.
  • Give age-specific risks:
    • Age at CVS: ____________
    • Down syndrome: 1 in _______ ( %)
    • Any CA: 1 in ________ ( %)

Discuss the option of CVSEdit

  • What is it?
    • CVS is short for chorionic villus sampling
    • The chorionic villi are wisps of fetal tissue or finger-like projections that attach the pregnancy sac to the uterine wall
    • CVS is the technique in which this sample of placental tissue is obtained
    • The technique has been around for approximately 15 years although methods have changed over time
    • It is unique because it is used to diagnose certain birth defects in the 1st trimester of pregnancy rather than later in the pregnancy like amniocentesis
      • It is usually performed at 10-12 weeks gestation
  • What can it tell me?
    • CVS can detect certain abnormalities in the fetus
      • General chromosome abnormalities
      • Specific genetic disorders that have been previously identified
    • It can determine the sex of the baby.
  • What can it NOT tell me?
    • CVS cannot detect neural tube defects such as spina bifida
      • For this reason, it may be useful to measure the amount of AFP in the maternal serum at 15-18 weeks gestation
      • Also, follow-up with US at 18-20 weeks is recommended
    • It cannot detect all birth defects or mental retardation
      • For example, congenital heart defects, cleft lip & palate cannot be seen.
      • Also the severity of the defect cannot be known from CVS
  • Exactly what does the procedure involve?
    • Show figures of CVS
    • Transcervical CVS:
      • Done at 10-12 weeks gestation
      • A speculum is inserted and the vagina and cervix are cleaned with betadeine
      • Some physicians apply a tenaculum to the lip of the cervix which can be painful
      • Using US to guide, a thin tube is guided into the placenta
      • Gentle suction is applied to the tube to remove the villi
      • This method is easiest to perform when the placenta is posterior and close to the cervix
      • A larger sample is taken as compared to transvaginal CVS
      • Discomfort is often minimal, perhaps similar to a pap smear
      • Post-procedure bleeding occurs in up to 10% of patients
    • Transabdominal CVS:
      • Done at 10 weeks gestation or later
      • The abdomen is cleansed with betadeine
      • A local anesthetic injection may be given
      • Using US to guide, a spinal needed is inserted through the abdomen into the uterine wall and into the placenta
      • The needle is moved back and forth several times through the placenta
      • Suction is used to remove the villi sample
      • This method is easiest when the placenta is anterior or away from the cervix
      • This method is better for women with a retroverted uterus
      • A smaller sample (pieces of villi) is taken as compared to transcervical CVS
      • The procedure is usually more uncomfortable than the transcervical method
      • Bleeding after the procedure is rare
    • CVS takes approximately 5-7 minutes (not including prep time)
    • The baby's heartbeat is monitored by US
    • The collected sample is examined under the microscope to confirm that fetal tissue and not maternal tissue was collected
    • If maternal cells were collected, the CVS will be repeated
    • The sample is sent to the lab
    • Results are available in approximately 10 days
  • What will it feel like?
    • There may be some discomfort when the needle enters the skin and the uterus or when the catheter enters the cervix and placenta
    • Some say that they feel pressure during the procedure
    • You may experience a small amount of bleeding after CVS
  • What are the risks?
    • The background rate of pregnancy loss at 10-12 weeks is 2-3%
    • CVS increases the risk of miscarriage by 1/100 (1%) in women with a normal uterus
      • Reinforce that 99% of women will have a healthy baby
    • CVS increases the risk of miscarriage by 5/100 (5%) in women with a retroverted uterus using transcervical CVS
    • Some studies indicate an increased risk for limb defects when CVS is done before 10 weeks gestation
      • When performed at 10-12 weeks, most recent studies do not report an increased risk because limbs have already formed at this point
      • The risk is approximately 1/3000 (0.0003%)
    • There are special considerations for mothers who are Rh negative. They need to take RhoGam after the CVS procedure
    • There is a low risk of uterine infection
    • Exercise or strenuous activity is to be avoided for 24 hours after the procedure
    • Sexual intercourse, douching, tub baths, or tampon use are to be avoided for 72 hours after CVS procedure
    • CVS is not recommended for women with the following:
      • Cervical polyps, overly curved sampling pathway, active genital herpes (for trans-cer)
      • Interceding bowel, placenta too far from abdomen surface (for trans-abd)
      • Active vaginal bleeding or bleeding disorder
    • You should notify your doctor if any of the following occur:
      • Fever greater than 100.4 F
      • Heavy bleeding or cramping
      • Amniotic fluid leakage
  • Why should I choose CVS?
    • CVS can be done earlier than amniocentesis (10-12 weeks versus 15-18 weeks)
    • It may reduce a couples emotional stress if at risk for abnormality
    • The procedure allows for termination at an earlier age
      • This is before the pregnancy is visible
      • Also before fetal movement is felt
    • Allows for treatment of fetus affected with 21-hydroxylase deficiency
  • Why might I not want to choose CVS?
    • There is a higher risk for pregnancy loss as compared to amniocentesis
      • 1% for CVS versus 0.5% for amnio
    • CVS does not detect NTDs
    • CVS is less commonly done as compared to amnio
    • With CVS, there is a greater likelihood of needing further invasive testing due to:
      • Laboratory failure
      • Insufficient sample
      • Maternal cell contamination
        • Seen in approximately 1.9% of cases
      • Mosaic or ambiguous results
        • There are 2 or more cell types that are different genetically
        • Seen in 1-2% of CVS cases

Offer ResourcesEdit

  • Literature, contact info, etc.
  • March of Dimes website

Elicit final questions and concernsEdit

Reporting of the ResultsEdit

  • If they are having the procedure, discuss how they would like to receive the results
    • Appointment, phone call, etc.
    • Who will contact them?
  • Discuss the options: elective abortion, adoption, etc.


Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling

Heckert GNU white Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License."

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