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%