Handbook of Genetic Counseling/Advanced Maternal Age - Chorionic Villus Sampling (CVS)-3
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Advanced Maternal Age - Chorionic Villus Sampling
- 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
- Today's gestational age:_________
- How has this pregnancy been going?
- Any complications?
- Have you had an ultrasound?
- Date ________
- 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.
- 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 ________ ( %)
- 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:
- Shape of the head
- Intestinal problems
- 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
- 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
- Direct analysis: A preliminary answer
- 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.
- Risk of laboratory failure
- Maternal cell contamination
- 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
- 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
- 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.