Overview: Trisomy 18 TestIntroduction: The Trisomy 18 Test tests for trisomy 18 to diagnose Edwards syndrome, causing developmental issues in pregnancy, aiding in prenatal screening. Affecting 1 in 5,000 pregnancies, trisomy 18 poses diagnostic challenges due to severe outcomes. Following 2023 American College of Medical Genetics (ACMG) guidelines, it uses karyotyping/FISH for high accuracy, supporting cytogenetics screening. This test is vital for diagnosis, treatment planning, and improving outcomes in obstetrics.
Other Names: Edwards Syndrome Test, Trisomy 18 Screening Assay.
FDA Status: FDA-approved test, meeting cytogenetics standards for diagnostic reliability.
Historical Milestone: Trisomy 18 testing began in the 1960s with research by Edwards, who identified the condition. FISH advancements by Abbott improved detection, surpassing earlier karyotyping methods.
Purpose: Tests trisomy 18 status to diagnose Edwards syndrome, guides prenatal counseling or termination, and evaluates pregnancies with risk factors, aiming to inform decisions.
Test Parameters: Trisomy 18 status
Pretest Condition: Amniocentesis or blood sample required. Collect amniotic fluid or blood. Report pregnancy history.
Specimen: Amniotic Fluid (sterile container, 10-20 mL), Whole Blood (EDTA, 3-5 mL), Buccal Swab (sterile swab, 1-2 swabs), Saliva (sterile container, 1-2 mL); Amniotic fluid or 4 mL whole blood in EDTA tube. Transport in a biohazard container.
Sample Stability at Room Temperature: 24 hours
Sample Stability at Refrigeration: 48 hours
Sample Stability at Frozen: Not recommended
Medical History: Document pregnancy or family history. Include current medications or ultrasound findings.
Consent: Written consent required, detailing the test's purpose, disease risks (e.g., stillbirth), and sample collection risks.
Procedural Considerations: Uses karyotyping/FISH to detect trisomy, requiring labs with cytogenetic expertise. Results available in 5-7 days. Performed in labs with strict handling.
Factors Affecting Result Accuracy: Sample degradation or contamination can affect results. Medications may not affect results but require correlation.
Clinical Significance: Positive status confirms Edwards syndrome, guiding counseling. Early detection might inform decisions, while untreated cases lead to fetal loss. Normal status may require monitoring.
Specialist Consultation: Consult an obstetrician or genetic counselor for interpretation.
Additional Supporting Tests: Ultrasound, NIPT, or AFP to confirm diagnosis.
Test Limitations: Specific to trisomy 18; correlation with clinical status needed. False negatives possible with mosaicism.
References: ACMG Guidelines, 2023; Lancet, Edwards JH, 2022.
