# 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

## Medical/Family History

* 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

* 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

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

## Options

* 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

* 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

* 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

* 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

* 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

* 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

* 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

* 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

The information in this outline was last updated in 2001.