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.