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

Advanced Maternal Age - Chorionic Villus Sampling

Contracting

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

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?

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

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

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

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.

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

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.

The information in this outline was last updated in 2001.