Zygosity Testing

Zygosity testing is available to evaluate whether twins are monozygotic or dizygotic based on the presence of specific alleles from a panel of highly-polymorphic short tandem repeat (STR) markers. Template DNA will be extracted from the twins, the mother and the father. STR allele profiles are then established for each individual. The informative STRs are then used in Bayesian calculations to determine the likelihood for monozygotic or dizygotic twinning.

Indications for Testing

  • Twin pregnancy with medical issue
  • Twin delivery with medical issue
  • Medical issue in one twin
  • Parental concern

Sample Requirements

Note: parental blood samples are preferred as well.

  • Blood: Infants: 2-3 mL whole blood in purple top EDTA tube
  • Children (>2 years) and adults: 3-4 mL whole blood in purple top EDTA tube
  • Amniotic fluid or cultured amniocytes
  • Chorionic villi or cultured chorionic villi cells

Sample Handling

Sample should be kept at room temperature. Specimens being sent from outside facilities should be packaged according to standard medical safety practices. The specimen should never be frozen. The specimen should be shipped overnight priority.

For local samples, please call Client Service (216-844-5227) to arrange for sample pick-up.

Turnaround Time

Three to nine days

CPT Code


Please submit a completed Molecular Requisition for each sample.