How effective is chorionic villus sampling for down syndrome?

Chorionic villus sampling, often called CVS, collects a small sample of tissue from the placenta. The cells can be analysed for chromosome differences, including the extra chromosome associated with Down syndrome. Because the sample comes from the placenta, the result is highly informative but may occasionally need clarification if placental cells and the baby's cells do not match exactly. Your specialist will explain whether the laboratory uses a rapid result, a fuller analysis, or both.

CVS is a diagnostic procedure rather than a screening test. It does not assess every genetic condition or predict a child's health, development or future needs. Counselling before and after testing helps you understand the scope of the result.

Discuss why CVS has been offered, what conditions the laboratory will examine, when results are expected, and what an uncertain or unexpected result could mean. Ask about the procedure route, pain relief, infection precautions and the follow-up plan. Take time to consider how you would use the information; a genetic counsellor can support this discussion. Screening results, ultrasound findings and family history may all form part of the decision.

Follow the unit's aftercare instructions and seek urgent maternity advice for heavy bleeding, severe or worsening abdominal pain, fever, chills, fluid leakage, fainting, or feeling acutely unwell. These symptoms need assessment after an invasive pregnancy procedure and should not be judged from the test result alone.

Ask: What did my screening or ultrasound show? Which chromosome conditions will CVS assess? Could the result need confirmation? When and how will results be shared? What choices and support would be available after each possible result?