2024 Edition

Twin Zygosity DNA Test Guide

Twin Zygosity DNA Test Summary
What: A twin zygosity test is used to find out if twins are fraternal or identical.
Who: Anyone who wants to confirm their relationship with their twin or parents who are curious about their children can order a twin zygosity test.
Where: DNA tests are available online to anyone in the world.
When: A twin zygosity test can be done any time after the children are born.
How: DNA is analyzed to see if it is identical. Identical twins share identical DNA, while fraternal twins do not.
Type: DNA is collected with a cheek swab.
Why: A twin zygosity test offers conclusive evidence that twins are identical or fraternal.
Time: Test results take approximately five to seven days.
Language: Not applicable.
Preparation: Prior to a cheek swab, one should rinse their mouth with water.
Cost: DNA test costs range from $99 to $400 for twins; additional children can be tested for $75 to $150 per person.

By: Erin Hasinger, Tests.com


A twin zygosity DNA test is used to determine whether twins, triplets or other form of multiples are identical or fraternal. At birth, the doctor can examine the placenta to make this determination; identical twins share a placenta while in utero, while fraternal twins do not.


A twin DNA test provides absolute certainty about the twins’ relationship, which is helpful when a doctor is unable to make a conclusive determination, or if parents have questions about their children as they age. For example, twins thought to be fraternal at birth may grow up to look identical. Conversely, twins thought to be identical may grow up to look very different. A DNA test can provide absolute confirmation that the children are either fraternal or identical.


Identical twins come from the same zygote, or fertilized egg. The zygote splits to form two or more embryos, and as a result, identical twins share the same DNA. Fraternal twins develop when two eggs are fertilized by two sperm, which means their DNA will be different. During a twin zygosity DNA test, the twins’ DNA samples will be compared. If the DNA is identical, the twins are determined to be identical. If the DNA shares similarities but is not identical, much like regular siblings, the twins are determined to be fraternal.


A twin zygosity DNA test can be performed any time after the children are born. DNA samples are collected from each child using a buccal swab, which is done with a cotton swab swiped across the inside of one’s cheek. DNA is extracted from the collected cells in a laboratory and then is compared.


Twin zygosity DNA test kits are readily available for purchase worldwide, and many companies sell DNA test kits online. After the order is placed, a test kit is mailed to the user. Each participant provides a DNA sample through a cheek swab, and the cotton swab used is then mailed back to the laboratory according to the company’s instructions. The lab will analyze the DNA and make a determination about the twins’ relationship. If the DNA test is being done for legal reasons, the laboratory will be able to help establish a chain of custody and witnesses so that the results are considered usable in court.


Generally, test results take about five to seven days, and the company will either provide an official report through the mail or make the results available online through a secure website. Note that it is important to choose a company whose laboratory is accredited by the American Association of Blood Banks when proceeding with any kind of DNA test.


Costs for a twin zygosity test vary among different companies, but the range is generally between $99 and $400 for twins. Most companies will test triplets, quadruplets and other multiples for an additional fee; those fees range from $75 to $150 per child.


For more on twin zygosity tests or to locate a home test kit, see the Twin Zygosity DNA Test Directory.


Sources: American Pregnancy Association, DNA Center, Easy DNA