Amniocentesis vs CVS: Differences, Risks & When They’re Recommended Procedure-Focused Posts

Advances in prenatal care allow doctors to identify genetic and chromosomal conditions early in pregnancy. When screening tests show an increased risk, expectant parents may be advised to consider Amniocentesis and CVS testing. These are diagnostic procedures, meaning they can provide definitive answers rather than risk estimates.

Understanding the differences between amniocentesis and chorionic villus sampling (CVS), their risks, and when each is recommended can help parents make informed and confident decisions.

What Are Diagnostic Prenatal Tests?

Unlike screening tests such as NT scan or NIPT, diagnostic tests analyze fetal cells directly to confirm or rule out genetic and chromosomal conditions. The two most commonly used diagnostic procedures are:

• Chorionic Villus Sampling (CVS)

• Amniocentesis

Both tests detect conditions like Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), Patau syndrome (Trisomy 13), and certain inherited genetic disorders.

What Is Chorionic Villus Sampling (CVS)?

CVS is a diagnostic test performed earlier in pregnancy, usually between 11 and 14 weeks.

How CVS Is Done

A small sample of placental tissue (chorionic villi) is collected using:

• A thin needle through the abdomen (transabdominal), or

• A catheter through the cervix (transcervical)

The placental cells share the same genetic makeup as the fetus, allowing accurate genetic analysis.

What CVS Can Detect

• Chromosomal abnormalities

• Certain inherited genetic disorders

However, CVS does not detect neural tube defects, which require later testing.

What Is Amniocentesis?

Amniocentesis is typically performed later, between 15 and 20 weeks of pregnancy.

How Amniocentesis Is Done

Using ultrasound guidance, a thin needle is inserted through the abdomen to withdraw a small amount of amniotic fluid. This fluid contains fetal cells, which are then analyzed in the laboratory.

What Amniocentesis Can Detect

• Chromosomal abnormalities

• Genetic disorders

• Neural tube defects (through AFP levels)

  
  

Amniocentesis vs CVS: Key Differences

Timing

• CVS: 11–14 weeks

• Amniocentesis: 15–20 weeks

Sample Collected

• CVS: Placental tissue

• Amniocentesis: Amniotic fluid

Detection Scope

• CVS: Chromosomal and genetic disorders

• Amniocentesis: Chromosomal, genetic, and neural tube defects

Results Availability

• CVS: Earlier results, allowing early decision-making

• Amniocentesis: Slightly later but broader diagnostic information

  
  

Risks Associated With Amniocentesis and CVS Testing

Both procedures are generally safe when performed by experienced fetal medicine specialists, but they do carry small risks.

Common Risks Include:

• Mild cramping after the procedure

• Spotting or fluid leakage (rare)

• Infection (very rare)

Miscarriage Risk

• CVS: Approximately 0.5–1%

• Amniocentesis: Approximately 0.1–0.3%

Your doctor will carefully explain individual risk based on medical history and scan findings.

When Are These Tests Recommended?

Doctors may recommend Amniocentesis and CVS testing in the following situations:

• High-risk results from NT scan, NIPT, or biochemical screening

• Advanced maternal age (35 years or older)

• Previous pregnancy affected by a genetic condition

• Known family history of inherited disorders

• Structural abnormalities detected on ultrasound

The choice between CVS and amniocentesis depends on gestational age, type of suspected condition, and parental preference.

Which Test Is Right for You?

There is no single “better” test—it depends on individual circumstances:

• CVS may be preferred if early diagnosis is important

• Amniocentesis may be preferred if neural tube defects need evaluation or if CVS timing has passed

Genetic counselling is strongly recommended before undergoing either procedure to fully understand benefits, risks, and alternatives.

Emotional Support and Counselling

Facing the decision to undergo diagnostic testing can be emotionally challenging. Genetic counsellors and fetal medicine specialists help parents:

• Understand complex medical information

• Process emotions and concerns

• Make informed, pressure-free decisions

Supportive counselling is a crucial part of prenatal diagnostic care.

Conclusion

Both amniocentesis and CVS are valuable diagnostic tools that provide clear answers when screening tests raise concerns. While each test differs in timing, method, and scope, both play an important role in modern prenatal care. Understanding the differences, risks, and indications for Amniocentesis and CVS testing allows expectant parents to approach these decisions with knowledge, confidence, and support—ensuring the best possible care for mother and baby.

FAQs

1. Are amniocentesis and CVS mandatory?

No. These tests are optional and are recommended based on individual risk factors and screening results.

2. Which test is safer: CVS or amniocentesis?

Both are safe when done by specialists, but amniocentesis has a slightly lower miscarriage risk.

3. How long does it take to get results?

Initial results may take 3–7 days, while detailed genetic analysis can take up to 2–3 weeks.

4. Can these tests harm the baby?

Serious complications are rare. Your doctor will explain risks in detail before the procedure.

5. Is genetic counselling necessary before these tests?

Yes. Genetic counselling helps you understand the need, risks, and implications of the results.

Reference Links

• https://www.acog.org/womens-health/faqs/amniocentesis

• https://www.nhs.uk/conditions/amniocentesis/

• https://www.mayoclinic.org/tests-procedures/amniocentesis/about/pac-20392914

• https://www.cdc.gov/ncbddd/birthdefects/diagnosis.html

• https://medlineplus.gov/chorionicvillusampling.html