# Handbook of Genetic Counseling/Advanced Maternal Age - Chorionic Villus Sampling (CVS)-2

Advanced Maternal Age - Chorionic Villus Sampling (CVS)

## Contracting

* How has your pregnancy been going? Have there been any complications?
* What is your understanding of why you were referred for genetic counseling?
* What specific questions/concerns would you like to address today?

## Maternal Age Associated Pregnancy Risks

* Women over age of 35 considered at "high risk" for chromosomal abnormalities
* Explain chromosomes and nondisjunction
* Common trisomies associated with advanced maternal age
** Trisomy 21 (Down Syndrome)
*** Caused by presence of 3 copies of chromosome 21
*** Can result in characteristic facies, mild to moderate mental retardation, congenital heart disease and other health problems
*** Varying range of severity
*** Many children can go to school, adults may hold jobs and live semi-independently
** Trisomy 13 (Patau Syndrome) and Trisomy 18 (Edward Syndrome)
*** Caused by presence of 3 copies of chromosome 13 or 18
*** More severe medical issues than those associated with Down Syndrome
*** Usually fatal within first year of life
** Klinefelter Syndrome (47,XXY)
*** Caused by presence of an extra X chromosome
*** Phenotypic males who may have small testes and androgen deficiency
*** IQ may be 10-15 points lower than average

## Testing Options

* Triple marker screening
** Blood test performed at 15-22 weeks gestation
** Screening test, not diagnostic
*** In whole population, detects 62% of problems
*** False positive rate of 3.6%
** Indirect measurement of AFP, hCG, and uE3 production
** Detects some chromosomal abnormalities associate with maternal age
*** Down Syndrome (70% in women older than 35)
*** Trisomy 18 (60%)
*** Open neural tube defects (80-90%)
*** Does not detect all chromosomal abnormalities associated with maternal age
** Amniocentesis may be offered to follow-up on results
* Ultrasound
** Capable of detecting many major birth defects
*** May identify ultrasound anomaly that could indicate a chromosomal abnormality
*** Cannot diagnose chromosome abnormality based on ultrasound findings
** Amniocentesis or CVS may be offered to follow-up on results
* Chorionic Villus Sampling (CVS)
** Sample of placental tissue (chorionic villi) obtained
*** Tissue is from same embryonic origin as fetus
*** Should have same genetic composition as fetus
** Usually performed at 10-12 weeks gestation
** Technique
*** Transcervical
**** Begin with ultrasound exam to confirm fetal heart activity, appropriate growth, and location of placenta, uterus, and cervix
**** Patient placed in lithotomy position
**** Vagina and cervix cleaned with betadeine
**** Speculum is inserted and some physicians apply a tenaculum to the lip of the cervix to help manipulate the uterus
**** Catheter with a stylet inserted is guided into the placenta using US
**** Stylet removed and syringe inserted
**** Suction is applied to aspirate villi
**** May be slightly uncomfortable
*** Transabdominal
**** Begin with ultrasound exam
**** Abdomen cleaned with betadeine and xylocaine injection given to numb skin
**** Spinal needle with stylet guided through abdominal and uterine walls into placenta using ultrasound guidance
**** Stylet removed and syringe attached
**** Suction applied by syringe plunger and needlemoved back and forth
**** Can be performed at any time during pregnancy
**** May be moderately uncomfortable
*** Transcervical vs. transabdominal
**** Bleeding more common following transcervical (10%)
**** Cramping more common following transabdominal
**** No significant difference in risk for fetal loss
**** Some reports indicate transcervical may have higher risk for infection
*** Recommendations for medical care
**** Rh negative women should be given Rhogam
**** No exercise or strenuous activity for 24 hours
**** No sexual intercourse, douching, tub baths, or use of tampons for 72 hours
**** Notify OB if any of the following signs
***** Fever above 1000F
***** Heavy bleeding or cramping
***** Amniotic fluid leakage
**** Follow up ultrasound in a few days
**** MSAFP at 16-18 weeks
**** Ultrasound at 20 weeks to check fetal anatomy
** Risks/Benefits of CVS
*** 98-99% accuracy for fetal chromosome analysis
**** Allow identification of affected fetus early in pregnancy
**** Maternal cell contamination risk if 46,XX result
**** 1-2% chance for mosaicism
***** Presence of two or more cell lines that differ in chromosome composition
***** Difficult to interpret because may arise in vitro in lab, may be confined to placenta and not affect fetus, or may represent true fetal mosaicism
*** Can perform molecular DNA analysis or biochemical analysis if at risk fetus
*** Can't detect open neural tube defects
*** Can't detect all birth defects or mental retardation
*** Risk of miscarriage due to procedure is 1% (in addition to 2-3% background risk)
*** Some past studies have cited increased risk for transverse limb anomalies
**** When performed before 10 weeks
**** More recent studies do not indicate any increased risk when performed at 10-12 weeks
*** Some women with elevated MSAFP or unclear CVS results may be offered amniocentesis
*** Not recommended for women with following conditions
**** Active vaginal bleeding
**** Maternal bleeding disorder
**** Cervical polyps, active genital herpes or other infection (transcervical)
**** Interceding bowel or placenta far from maternal abdominal surface (transabdominal)

## Amniocentesis

* Performed after 15 weeks
* Risks/Benefits
** 99.7% accuracy for fetal chromosome analysis
** Detects 96% of open neural tube defects by testing AFAFP
** Cannot detect all birth defects or mental retardation
** Risk of miscarriage due to procedure is 0.5%
** Incidence of mosaicism is 0.1-0.3%

## Notes

The information for this outline was last updated in 2001.