In a 38‑week stillbirth with a normal‑appearing placenta and fetus, which specimen is most appropriate for chromosomal analysis?

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Umbilical Cord Sampling is the Best Specimen for Chromosomal Analysis in Stillbirth

In a 38-week stillbirth with normal-appearing placenta and fetus, umbilical cord blood should be collected for chromosomal analysis, as it represents the most reliable specimen for fetal karyotyping and avoids the pitfalls of confined placental mosaicism. 1

Why Umbilical Cord Blood is Preferred

Direct Fetal Representation

  • Fetal cord blood is the standard specimen for postnatal chromosomal analysis because it directly reflects fetal chromosomes, not maternal or placental tissue that may harbor mosaicism 1
  • Blood chromosome analysis from the umbilical cord should be performed even when prenatal testing was normal, as mosaicism may have been undetected or banding resolution may be higher in postnatal preparations 1
  • The American College of Medical Genetics and Genomics specifically recommends collecting blood from the fetal (umbilical) cord for postnatal chromosomal analysis when the infant has been delivered and requires karyotyping 1

Critical Pitfall to Avoid

  • Maternal cord blood reflects maternal chromosomes, not fetal chromosomes, making it useless for fetal genetic diagnosis 1
  • You must ensure the specimen is collected from the fetal side of the umbilical cord, not from maternal vessels

Why Other Options Are Inferior

Amniotic Fluid (Option B) - Not Accessible Postnatally

  • Amniotic fluid is not suitable for postnatal testing as it is a prenatal specimen collected before delivery via amniocentesis 1
  • After delivery in a stillbirth case, amniotic fluid is no longer accessible or relevant for postnatal testing 1
  • While amniotic fluid would have been excellent for prenatal diagnosis, the question specifically addresses a delivered stillborn infant 2

Fetal Cord Blood (Option C) - May Be Non-Viable

  • In cases of fetal demise, especially when a substantial interval has elapsed after death, fetal cord blood may be unavailable or non-viable for DNA extraction 2
  • This is essentially the same as umbilical cord sampling (Option A), but the viability concern makes it less reliable in stillbirth cases where tissue degradation has occurred

Placental Tissue (Option D) - Confined Placental Mosaicism

  • Fresh placental tissue has significantly lower success rates for chromosomal analysis, and extensive testing of placental tissue is not recommended as it may not be representative of the actual fetal chromosomes 2
  • Confined placental mosaicism (CPM) is a major limitation, occurring in approximately 2% of viable pregnancies, where chromosomal abnormalities are present in the placenta but not in the fetus 3
  • Placental tissue may show chromosomal abnormalities not present in the fetus, or vice versa, leading to false-positive or false-negative results 2
  • Formalin-fixed paraffin-embedded placental tissue is not accepted by many genetic testing laboratories because it yields significantly lower success rates 2

Practical Collection Guidelines

Specimen Handling

  • Collect specimens as soon as possible after diagnosis of demise, with documentation of time of collection after death and storage conditions for laboratory acceptance 2
  • Clean skin with alcohol only, never iodine-containing compounds, as iodine inhibits cell culture growth 2
  • Transport fresh tissue on ice or with dry ice if previously frozen 2

If Umbilical Cord Blood Fails

  • If peripheral blood analysis is normal but clinical suspicion remains high for chromosomal abnormality, skin fibroblast culture can detect mosaicism that may not be present in circulating T-lymphocytes 1
  • Skin fibroblasts are particularly valuable for detecting mosaicism that may not be present in other tissues 2
  • Certain chromosomal abnormalities are only detectable in fibroblasts 1

Clinical Context for Stillbirth Investigation

  • Chromosomal abnormalities are recognized as one of the major causes of stillbirth that should be investigated through a complete stillbirth workup 4
  • All major guidelines (ACOG, RCOG, PSANZ, SOGC) recommend genetic analysis as part of stillbirth investigation, with consensus that determining the etiology may improve care in a subsequent pregnancy 5
  • A minimum 550-band resolution is indicated for newborns with dysmorphic features or suspected chromosomal abnormalities 1

Answer: A. Umbilical cord sampling

References

1
Guideline

Postnatal Chromosomal Analysis

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

2
Guideline

Chromosomal Analysis in Fetal Stillbirth

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

3
Research

Confined placental mosaicism.

Journal of medical genetics, 1996

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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