amniocentesis
Summary
Amniocentesis is a prenatal diagnostic procedure involving transabdominal needle insertion into the amniotic sac to extract amniotic fluid for genetic and chromosomal analysis. Typically performed between 15-20 weeks gestation, it carries a small risk of miscarriage (<0.1-0.3%) but provides definitive diagnosis of fetal abnormalities.
Detail
Amniocentesis involves ultrasound-guided insertion of a thin needle through the maternal abdomen and uterine wall into the amniotic cavity to aspirate 15-20 mL of amniotic fluid. The fluid contains fetal cells that can be analyzed for chromosomal abnormalities (trisomy 21, 18, 13), genetic disorders (cystic fibrosis, sickle cell disease), and neural tube defects (via alpha-fetoprotein levels). The procedure is typically offered to women with increased risk factors including maternal age ≥35, abnormal maternal serum screening, abnormal ultrasound findings, or family history of genetic disorders. Complications are rare but include infection, bleeding, leakage of amniotic fluid, and pregnancy loss (risk <0.1-0.3%). The procedure provides >99% accuracy for chromosomal abnormalities. Results are usually available within 1-2 weeks, allowing for informed decision-making about pregnancy management.
Sources
- Williams Obstetrics 25th Edition
- ACOG Practice Bulletin No. 162: Prenatal Diagnostic Testing
- First Aid for the USMLE Step 2 CK
- Obstetrics and Gynecology by Beckmann
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