Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1147 page)

   Provides placental material for chromosome (cytogenetic) testing, biochemical testing (metabolic disorders/inborn errors of metabolism), and molecular DNA-based testing for inherited disease (e.g., cystic fibrosis, fragile X).

   Primary advantage over amniocentesis is earlier time frame, allowing pregnancy termination in the first trimester or earlier relief of anxiety.

   Limitations

   Chromosome results may be ambiguous due to confined placental mosaicism (abnormal chromosome line limited to placental tissue) in approximately 2% of cases, requiring follow-up by amniocentesis

   Maternal cell contamination must be avoided for accurate diagnosis based on fetal chromosomes, enzyme assay, or DNA analysis

   Does not provide material to screen for neural tube defects

FETAL BIOPSY
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   Definition

   Invasive procedure to obtain fetal tissue such as skin, muscle, or liver.

   Use

   Diagnosis of specific inherited disorders when gene mutation is unknown

   Liver biopsy for specific inherited metabolic disorders (e.g., ornithine transcarbamylase deficiency, carbamoyl phosphate synthetase deficiency, G6PD [type 1a])

   Skin biopsy for specific genetic skin disorders (e.g., epidermolysis bullosa)

   Muscle biopsy for Duchenne muscular dystrophy