Amniocentesis
Amniocentesis is a diagnostic procedure that analyzes amniotic fluid to provide a definitive chromosomal diagnosis. It's offered when screening tests suggest increased risk or when parents want definitive information.
Typically performed: Weeks 15–20 (or later if indicated)
What It Tests For
Amniocentesis can detect chromosomal conditions (Down syndrome, Trisomy 18, Trisomy 13), genetic disorders, and certain infections. It provides a karyotype (full chromosome picture) and can include microarray analysis for smaller genetic changes. Results are typically available in 7–14 days.
The Procedure
An ultrasound guides a thin needle through the abdomen into the amniotic sac. A small amount of fluid (about 2 tablespoons) is withdrawn. The procedure takes about 1–2 minutes. Local anesthetic is offered. Most people experience cramping similar to menstrual cramps during and after the procedure.
Risks
The procedure-related miscarriage risk is approximately 0.1–0.3% (1 in 300–1,000) at experienced centers. Other risks include cramping, spotting, leaking of fluid, and very rarely infection. Post-procedure, rest is recommended for 24 hours.
Frequently Asked Questions
Most people describe pressure and cramping rather than sharp pain. The needle insertion is brief. Post-procedure cramping for a few hours is common.
Yes — all procedures are your choice. Some parents act on NIPT results without diagnostic confirmation; others want the certainty that only amniocentesis provides. Genetic counseling can help you decide what information you need.
CVS (chorionic villus sampling) is done earlier (10–13 weeks) and tests placental cells rather than amniotic fluid. Amniocentesis is done at 15–20 weeks and tests amniotic cells. Both provide chromosomal diagnosis; amniocentesis is slightly more accurate and tests for more conditions.