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Genetic counseling: Advanced Maternal Age - Chorionic Villus Sampling (CVS)-2

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Advanced Maternal Age - Chorionic Villus Sampling (CVS)

ContractingEdit

  • 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 RisksEdit

  • 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-independantly
    • 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 OptionsEdit

  • 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)

AmniocentesisEdit

  • 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%

NotesEdit

The information for this outline was last updated in 2001.



Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling

Heckert GNU white Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License."

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