Amniocentesis is an invasive diagnostic procedure in which a needle is inserted into the amniotic sac under ultrasound guidance to withdraw amniotic fluid for testing.
Indications for Amniocentesis
1. Genetic & Chromosomal Testing (Common Indication)
- Detection of chromosomal abnormalities (Trisomy 21, 18, 13).
- Diagnosis of genetic disorders (Thalassemia, Cystic fibrosis, Tay-Sachs disease).
- Fetal karyotyping in advanced maternal age (>35 years).
- Prenatal diagnosis of metabolic disorders.
2. Assessment of Fetal Lung Maturity
- Lecithin/Sphingomyelin (L/S) Ratio >2 → Indicates lung maturity.
- Phosphatidylglycerol (PG) presence → Confirms lung maturity.
3. Diagnosis of Fetal Infections
- TORCH Infections (Toxoplasmosis, Rubella, CMV, Herpes).
- Chorioamnionitis detection (Culture & PCR of amniotic fluid).
4. Management of Hemolytic Disease of the Fetus (Rh Isoimmunization)
- Measure bilirubin levels (Delta OD 450) in Rh-negative mothers.
5. Polyhydramnios & Oligohydramnios Evaluation
- Detects fetal anomalies causing excess or reduced amniotic fluid.
Procedure of Amniocentesis
1. Timing:
- Genetic Screening: Performed at 15–20 weeks gestation.
- Fetal Lung Maturity Testing: Performed at >32 weeks gestation.
2. Technique:
- Ultrasound guidance to locate amniotic sac.
- Sterilization of abdominal area.
- Insertion of a fine needle into the amniotic sac.
- Aspiration of 15–20 mL of amniotic fluid.
- Fluid sent for biochemical, genetic, or microbiological analysis.
Complications of Amniocentesis
Maternal Risks:
- Abdominal pain & cramping.
- Amniotic fluid leakage.
- Infections (Chorioamnionitis – Rare).
Fetal Risks:
- Miscarriage (<1% risk, higher if done <15 weeks).
- Fetal injury (Rare with ultrasound guidance).
- Preterm labor (If done in late pregnancy).
Contraindications of Amniocentesis
- Placenta previa (Risk of bleeding).
- Active maternal infections (HIV, Hepatitis B, HSV).
- Unstable maternal condition (Preterm labor, Preeclampsia).
Alternatives to Amniocentesis
- Chorionic Villus Sampling (CVS): Done at 10–13 weeks for early genetic diagnosis.
- Non-Invasive Prenatal Testing (NIPT): Blood test for fetal DNA (No miscarriage risk).
Summary Table: Amniocentesis
|
Feature |
Details |
|
Timing |
15–20 weeks (Genetic), >32 weeks (Lung Maturity) |
|
Indications |
Chromosomal disorders, Rh Isoimmunization,
Infections, Lung Maturity |
|
Procedure |
Ultrasound-guided fluid aspiration |
|
Complications |
Miscarriage, Infection, Preterm labor |
|
Contraindications |
Placenta previa, Maternal infections |
|
Alternatives |
CVS, NIPT |
Key Takeaways
- Amniocentesis is a key test for genetic screening & fetal lung maturity.
- It carries a small risk of miscarriage (<1%).
- Safer alternatives like NIPT exist but are not diagnostic.
- Ultrasound guidance reduces fetal injury risk.
