Chromosomal Analysis in Stillbirth at 28 Weeks
Amniotic fluid sampling (Option B) is the most indicated method for diagnosing chromosomal abnormalities in this stillbirth case, with an 83% success rate for karyotyping and 100% success rate for chromosomal microarray analysis. 1
Tissue Selection for Chromosomal Analysis
The choice of tissue for genetic testing in stillbirth directly impacts diagnostic success:
- Amniotic fluid demonstrates the highest success rate at 83% for conventional karyotyping and can be obtained via amniocentesis even after fetal demise 1
- Placental tissue shows 78% success for karyotyping, making it a reasonable alternative if amniocentesis cannot be performed 1
- Fetal cord blood has only 6.3% success rate due to cell death and hemolysis in stillbirth 1
- Umbilical cord tissue sampling is not a standard diagnostic approach and lacks supporting evidence in the literature provided
- Fetal skin biopsy shows only 13% success rate for karyotyping 1
Optimal Testing Strategy
Chromosomal microarray analysis (CMA) on amniotic fluid is the preferred diagnostic approach because:
- CMA achieves 100% success rate regardless of tissue type sampled 1
- CMA detects both full/partial aneuploidies (3.9% prevalence) and submicroscopic abnormalities (5.3% prevalence) that conventional karyotyping would miss 1
- Amniotic fluid contains viable cells even after fetal demise, unlike fetal blood or skin 1
Clinical Implementation
When managing this stillbirth case:
- Perform amniocentesis to obtain amniotic fluid as the primary tissue source 1
- Request both CMA and conventional karyotyping if available, as CMA provides superior diagnostic yield 1
- If amniocentesis is technically impossible, placental tissue is the second-best option with 78% karyotyping success 1
- Avoid fetal cord blood sampling (Option C) as it has the lowest success rate at 6.3% 1
Common Pitfalls
- Do not rely on fetal blood sampling in stillbirth—cell viability is severely compromised after fetal death 1
- Placental tissue may show confined placental mosaicism, which does not reflect true fetal karyotype 2
- Conventional karyotyping alone misses submicroscopic deletions and duplications that account for additional 5.3% of abnormalities 1