Amniocentesis: Understanding the Procedure and Benefits

Amniocentesis is a prenatal diagnostic procedure (typically 15–20 weeks) where a thin needle, under ultrasound guidance, withdraws ~20 mL amniotic fluid for fetal cell analysis.

Primary Indications

1. Advanced Maternal Age (≥35): Increased aneuploidy risk.
2. Positive Screening: cfDNA (NIPT), first-trimester combined, quad screen.
3. Fetal Anomalies on Ultrasound: Structural (heart, brain, spine) or soft markers.
4. Parental Chromosomal Rearrangement: Balanced translocation carrier.
5. Previous Affected Pregnancy: Aneuploidy or genetic disorder.
6. Genetic Disorder Risk: Known familial mutation (cystic fibrosis, sickle cell, Tay-Sachs).
7. Fetal Infection: CMV, toxoplasmosis, parvovirus, Zika (PCR on fluid).
8. Rh Alloimmunization: Assess fetal anemia (ΔOD450).
9. Fetal Lung Maturity: Rare now; L/S ratio, PG, lamellar body count if delivery <39 weeks without confirmed dates.

Procedure & Risks

• Outpatient, ultrasound-guided, ~30 min.
• Risks: Miscarriage ~0.1–0.3% (1:300–1:1000), leakage, infection, needle injury (rare), Rh sensitization (RhIg given if Rh-neg).
• Results: FISH/rapid aneuploidy (2–3 days), karyotype (1–2 weeks), microarray (2–3 weeks).

Decision-Making

Non-invasive prenatal testing (NIPT/cfDNA) is screening only—high sensitivity/specificity but not diagnostic. Amniocentesis provides definitive karyotype. Decision is personal; genetic counseling supports informed choice.