Zygosity testing is the process through which DNA sequences are compared to assess whether individuals born from a multiple gestation (twins, triplets, etc.) are monozygotic (identical) or dizygotic (fraternal).


PCR:  analysis for short tandem repeats for nine polymorphic loci.  Monozygosity can be excluded if both twins have inherited different polymorphic markers from their parents.  Monozygosity can be included at  > 99% if all markers tested are identical.

Specimen Requirements:

  • Blood: 6 mL EDTA (purple-top) or ACD (yellow-top) tube or
  • Amniotic fluid:  (Please call Client Services at (855) 535-1522 for sample size) or
  • Chorionic villi:  (Please call Client Services for sample size)
  • If sending DNA: please send 100ng at a minimum of 100ng/µL

A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES.  Please include detailed clinical information.

Test Performed (Days):


Turn Around Time:

7 – 10 Days

Shipment Sensitivity Requirements:

  • Package and ship specimen to remain cold, but not frozen. 
  • Ship via overnight express, using the FedEx priority overnight label provided. 
  • Contact Client Services for shipping kits and instructions at (855) 535-1522.


Additional Info:

This testing can also be medically important in the case of bone marrow and organ transplantation.  Please call Client Services at (855) 535-1522 for more information.

The Knight Cancer Institute at Oregon Health & Science University is a pioneer in the field of precision cancer medicine. The institute's director, Brian Druker, M.D., helped prove it was possible to shut down just the cells that enable cancer to grow. This breakthrough has made once-fatal forms of the disease manageable and transformed how cancer is treated. The OHSU Knight Cancer Institute is the only National Cancer Institute-designated Cancer Center between Sacramento and Seattle – an honor earned only by the nation's top cancer centers. It is headquarters for one of the National Cancer Institute's largest research collaboratives, SWOG, in addition to offering the latest treatments and technologies as well as hundreds of research studies and clinical trials.

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