Who needs to be tested?

One (1) set of twins

A twin zygosity test is a DNA test that definitively shows whether twins are identical or fraternal. When twins are born, the physician usually is able to tell whether they are identical or fraternal by examining the placenta. However, sometimes records can be lost, the placenta might have been discarded or damaged before twin zygosity was determined, or doubt may arise because of the twins’ physical characteristics. In such cases, only a DNA test can reveal the truth. A twin zygosity test compares the twins’ DNA profiles to see whether they match—an exact match proves  the twins are identical.

Turnaround Time

  • Two (2) business days from receipt of all samples

Chain-of-Custody Requirements

Chain-of-custody requirements must be fulfilled for test results to be defensible in any legal situation, such as inheritance disputes. These requirements include the following:

  • Samples are collected by a neutral third party, such as a clinic or laboratory
  • The individuals tested are positively identified (i.e., they present a government-issued ID to be photocopied and/or they are photographed and fingerprinted)
  • A standard DNA kit is used
  • Each party completes and signs a Client Identification and Consent Form
  • Guardianship of tested minor must be verified at the time of signing consent
  • The kit may not be in the possession of the clients prior to or after being collected

Non-Chain-of-Custody Requirements

In most cases, twin zygosity testing is used for personal knowledge only. In a non-chain-of-custody test, samples are collected by the patients themselves (or by collection site). Results of this test are for personal knowledge only and may not be used for legal purposes.

  • An in-home kit is used, and buccal samples can be collected by the patients themselves (or by collection site) at a time and place of their choosing
  • Since the origin of the samples cannot be verified, names are listed on the report in the same way they are labeled on the samples
  • A unique barcode is assigned to each kit and appears on the report as a reference for the case
  • Barcoded kits are assigned to your account for easy reference 


  • The results of a twin zygosity test may be used to satisfy personal curiosity as well as to help solve health problems for the twins later down the road. For example, in the event that a twin needs an organ- or tissue-transplant donor, the identical twin is a perfect choice
  • Identical twins come from one fertilized egg called a zygote. The zygote, which usually develops into one child, grows and splits early in development to form two embryos—identical twins. Because the twins come from one egg and one sperm, they have exactly the same DNA
  • Fraternal twins, develop when there are two different eggs in the mother’s womb that are fertilized by two different sperm. Fraternal twins will not have exactly the same DNA, although like other siblings, they can be expected to share some of the DNA they inherit from both parents