Zygosity Testing

Are you curious about whether you and your twin are identical or fraternal? If you are a male/female twin pair, you are definitely fraternal twins. However, if you are twins of the same sex, you might not be certain.

If you and your twin need zygosity results that are suitable for health-related purposes, please follow up with your healthcare provider to have a test performed by a CLIA-certified* laboratory.

If you want to know your zygosity only for curiosity and not to make medical decisions, there are commercial laboratories that offer direct-to-consumer zygosity testing. “Direct-to-consumer” means that you deal directly with the laboratory, without necessarily involving a doctor or an insurance company. The laboratory will mail you a home collection kit that you can use to collect cells from inside your cheeks. The collection process is easy and non-invasive. After you collect the cells, you will mail them back to the laboratory in the container provided. The laboratory will extract DNA from your cheek cells and use it to create your DNA profile.

A twin zygosity test compares the DNA profiles of a pair of twins at a number of markers (well-studied sequences of DNA) to see whether they match. If many of these markers are the same, then it is highly probable (i.e., greater than a 99% chance) that they are identical twins. If the twins are different at one or more markers, they are considered to be fraternal twins. The more markers studied, the more reliable the zygosity test results are.

Below we provide a partial list of laboratories that offer direct-to-consumer zygosity testing. The UW Twin Registry does not endorse any of these laboratories; we are simply providing examples of places that offer this service. Please contact the laboratories to ask about their current pricing and about any discounts that they may offer to members of the UW Twin Registry.

Affiliated Genetics
Location: Utah
Phone number: 1-800-362-5559
Number of markers analyzed: 15
Turnaround time for results: 7-10 working days
Discount for UW Twin Registry members?: Yes! Order by phone and identify yourself as a member of the UW Twin Registry
CLIA certified?*: Yes
AABB accredited?*: Yes

Proactive Genetics
Location: Georgia
Phone number: 1-866-427-1646
Number of markers analyzed: 15
Turnaround time for results: 10 working days
Discount for UW Twin Registry members?: Yes! Use the code ‘UWTR’ when ordering online or by phone
CLIA certified?*: No
AABB accredited?*: No

DNA Diagnostics Center (DDC)
Location: Ohio
Phone number: 1-800-613-5768
Number of markers analyzed: Minimum of 16, up to 18 if necessary
Turnaround time for results: 3 working days
Discount for UW Twin Registry members?: Yes! Use the code ‘UWTR’ when you call
CLIA certified?*: Yes
AABB accredited?*: Yes


*CLIA certification: sets certain federal standards for quality and competence. In the US, clinical laboratories must be CLIA-certified. Only testing done in a clinical laboratory (CLIA certified) should be used to make a medical diagnosis, or to develop a plan for prevention or treatment. Commercial zygosity testing laboratories do not have to be CLIA-certified,  although many are, because they also offer other testing that can be used for medical decisions. (CLIA = Clinical Laboratory Improvement Amendments)

**AABB accreditation: sets certain quality standards for laboratories that offer paternity testing and other kinds of relationship testing. It is not required for zygosity testing, but is required for paternity testing to be valid in court. (Note: AABB was originally an acronym for the American Association of Blood Banks, but in 2005 the organization announced that AABB is simply their name now and no longer signifies anything but itself.)