Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1148 page)

   Limitations

   High-risk procedures with value for a limited number of disorders

FETAL BLOOD SAMPLING (PERCUTANEOUS UMBILICAL BLOOD SAMPLING [PUBS], CORDOCENTESIS)
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   Definition

   Invasive procedure to obtain fetal blood generally performed after 18 weeks of gestation. Procedural risk of fetal loss is approximately 1–2%.

   Use

   Usually performed when diagnostic information cannot be obtained through amniocentesis, chorionic villus sampling (CVS), ultrasound examination, or following an inconclusive result from one of these tests

   Provides fetal material for chromosome (cytogenetic) testing, biochemical testing, and molecular DNA-based testing for inherited disease

   Chromosome analysis faster than with either amniocentesis or CVS because less culture time required; therefore, useful for late presentations

   Used to assess fetal isoimmunization (e.g., Rhesus factor, Kell), anemia, platelet count, hemolytic disease, and infection (e.g., toxoplasmosis, rubella, or CMV)

   May also be used to administer medication to the fetus

   Limitations

   Riskier procedure than amniocentesis of CVS performed late in pregnancy, limiting pregnancy termination options

   Does not assess neural tube defects