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.