Genetic counseling: Chorionic Villus Sampling (CVS)

Chorionic Villus Sampling (CVS)

Introduction

 * 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 Information

 * 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 History

 * 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?

 * 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 Abnormalities

 * 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 Risks

 * 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 CVS

 * 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 Resources

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

Reporting of the Results

 * 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