What is the Chorionic Villus Sampling (CVS) procedure?

Chorionic Villus Sampling (CVS) Procedure

Chorionic villus sampling (CVS) is a prenatal diagnostic procedure performed at 10-12 weeks' gestation that involves biopsying placental cells (chorionic villi) through either a transcervical or transabdominal approach to detect fetal genetic abnormalities, with a slightly higher risk of miscarriage (0.5-1.0%) compared to amniocentesis (0.25-0.50%) and a small risk of limb deficiencies (0.03-0.10%) when performed after 70 days' gestation. 1

Procedure Details

Timing and Approach

• CVS is typically performed between 10-12 weeks' gestation, earlier than amniocentesis (15-18 weeks), allowing for earlier diagnosis and decision-making 2, 1
• CVS should never be performed before 10 weeks (70 days) gestation due to significantly increased risk of limb deficiencies 1
• Two approaches are used for CVS collection 1:
  • Transcervical approach: A thin catheter is passed through the cervix under ultrasound guidance
  • Transabdominal approach: A needle is inserted through the abdominal wall under ultrasound guidance

Sample Collection Process

• The procedure begins with ultrasound localization of the developing placenta (chorion frondosum) 3
• For transcervical approach: A thin catheter is passed through the cervix into the chorion frondosum under real-time ultrasound guidance 3
• For transabdominal approach: A needle is inserted through the abdominal wall into the placenta 1
• Placental cells (chorionic villi) are obtained by gentle suction or aspiration 3
• These cells are derived from the same fertilized egg as the fetus, making them genetically identical for diagnostic purposes 2

Sample Processing

• The collected villi can be processed directly for chromosomal and/or biochemical analysis 3
• Initial results may be available within 6-24 hours for some tests 3
• Definitive results are confirmed by short-term cell cultures within 3-10 days 3
• Karyotyping of these cells is the standard method for diagnosing fetal aneuploidy 1

Safety Considerations

Miscarriage Risk

• CVS carries a miscarriage risk of approximately 0.5-1.0% (1/200-1/100) 2, 1
• This is slightly higher than the 0.25-0.50% (1/400-1/200) risk associated with amniocentesis 2, 1
• The risk of fetal loss increases with multiple catheter insertion attempts - 10.8% loss rate with 3-4 attempts versus 2.9% with a single attempt 4

Limb Deficiency Risk

• CVS has been associated with transverse limb deficiencies at a rate of 0.03-0.10% (1/3,000-1/1,000) 2, 1
• The risk and severity are directly related to timing 1:
  • CVS performed before 10 weeks has a higher risk (0.20%)
  • CVS performed at or after 10 weeks has a lower risk (0.07%), with most defects limited to digits
• Most birth defects reported after procedures performed at ≥70 days' gestation were limited to fingers or toes 2

Clinical Applications

• CVS is primarily used to detect 2, 1:
  • Chromosomal abnormalities (aneuploidy)
  • Genetic disorders detectable through molecular testing
  • Biochemical disorders
• Standard of care is to offer CVS or amniocentesis to women who will be ≥35 years at delivery due to increased risk of Down syndrome and other aneuploidies 2
• The risk of Down syndrome increases with maternal age: 1/385 (0.3%) at age 35 to 1/30 (3%) at age 45 2

Advantages and Limitations

Advantages

• Earlier diagnosis compared to amniocentesis (10-12 weeks vs. 15-18 weeks) 1, 5
• Allows for first-trimester termination if abnormalities are detected, which carries lower maternal morbidity and mortality than second-trimester procedures 1, 6
• Reduces parental anxiety by providing results earlier in pregnancy 3
• Particularly advantageous for detecting certain genetic conditions 2

Limitations

• Slightly higher miscarriage risk than amniocentesis (0.5-1.0% vs. 0.25-0.50%) 2, 1
• Small risk of limb deficiencies (0.03-0.10%) 2, 1
• Confined placental mosaicism occurs in approximately 1% of cases, which may require additional invasive testing 5
• Diagnostic accuracy is slightly lower than amniocentesis (97.8% vs. 99.4%) 4

Important Considerations

• The background risk for major birth defects for women of all ages is approximately 3% 2
• When counseling prospective parents about CVS, healthcare providers should discuss 2:
  • Benefits and risks of the procedure
  • Both parents' risks for transmitting genetic abnormalities
  • Alternative testing options, including amniocentesis
• The procedure should be performed by experienced providers to minimize risks 5
• Multiple catheter insertion attempts significantly increase the risk of fetal loss 4