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

Advanced Maternal Age - Chorionic Villus Sampling (CVS)

Contracting edit

How has your pregnancy been going? Have there been any complications?
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What specific questions/concerns would you like to address today?

Maternal Age Associated Pregnancy Risks edit

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 edit

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 edit

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 edit

The information for this outline was last updated in 2001.