Twin Zygosity Testing: Identical or Fraternal
Published January 30, 2026 · Medically reviewed by the partner laboratory's medical director, AABB-accredited relationship-testing laboratory
A twin zygosity DNA test compares STR markers between two twins to determine whether they share identical DNA (monozygotic/identical, from one fertilized egg) or share about 50% (dizygotic/fraternal, from two separate eggs). Cheek swabs, AABB-accredited lab, results in 1–2 business days.
Why it matters
Ultrasound and appearance are unreliable — same-sex fraternal twins can look nearly identical, and some identical twins develop distinct features. Zygosity testing is the only way to know for sure, and it matters for medical decisions (organ donation, disease risk) and personal identity.
Ready to move forward? Order our $99 at-home test — AABB-accredited, results in 1–2 business days.
The test
Two cheek swabs, one from each twin. The lab compares 24+ STR markers. Identical twins share every marker; fraternal twins show the expected variability of ordinary siblings.
How to order
Contact our team to arrange a zygosity kit — pricing is typically $149–$189 for the pair.