In brief — the direct answer
Amniocentesis and Chorionic Villus Sampling (CVS) are procedures used to obtain amniotic fluid or placental tissue for diagnostic laboratory testing. Unlike screening tests, they can answer specific diagnostic questions, but the certainty and scope depend on the test selected, the condition being investigated, sample quality, and interpretation. Both procedures use continuous ultrasound guidance and are offered after counselling about benefits, limitations, and risks.
What is Amniocentesis & CVS?
CVS samples placental tissue, usually at 11–14 weeks. Amniocentesis samples amniotic fluid and is generally offered from 15 completed weeks. The best procedure depends on gestation, the clinical question and whether placental mosaicism could affect interpretation. Rapid trisomy testing, karyotype, microarray and targeted gene tests answer different questions; the sample itself is not a test for every condition.
Who is at risk?
Diagnostic testing is not mandatory for every pregnancy, but it is often recommended if:
- A screening test (like NIPT or NT scan) has shown a high-risk result.
- An ultrasound has detected a structural anomaly in the baby.
- There is a known family history of a specific genetic condition (like Thalassemia or Cystic Fibrosis).
- The parents are known carriers of a genetic mutation.
How we diagnose it
Before sampling, the clinician confirms gestation, fetal and placental position, the testing plan, relevant infection results and blood group. A fine needle is guided using ultrasound. The appointment includes counselling, preparation and observation; sampling time and discomfort vary. Occasionally a second sample or a different test is needed.
What does management involve?
The team provides written aftercare, a contact pathway and laboratory-specific turnaround times. Seek prompt maternity advice for fluid leakage, fever, persistent or worsening pain, or significant bleeding after sampling. Anti-D is considered for an eligible RhD-negative patient according to the clinical protocol. Rapid results cover selected conditions; additional analyses can take longer and may produce uncertain or inconclusive findings.
What are the outcomes?
A diagnostic result applies to the conditions and methods actually tested. A normal result does not exclude all genetic, chromosomal or structural conditions, and ultrasound follow-up remains important. CVS can occasionally reflect confined placental mosaicism, prompting discussion of amniocentesis. Genetic counselling helps interpret a pathogenic, uncertain or unexpected result.
When to see a subspecialist
Arrange specialist counselling after a high-chance screen, a fetal finding, a known familial condition, or when you want to discuss diagnostic testing. The additional miscarriage risk is low but not zero and depends on the pregnancy, procedure and operator. Published estimates are not an audited outcome for this unit. Your clinician should explain the estimate relevant to you, the alternatives and the option to decline.