Twin DNA Testing
Are My Twins Identical Or Fraternal?

Genetic Tests

Identical or Not?

Twin DNA Testing


What Is A Twin DNA Test?
Why Test?
Why Are More People Testing?
When Can We Test?
How To Test

How Much Does It Cost?

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What Is A Twin DNA Test?

Also known as a twin zygosity test, this test is used to confirm if two (or more as in triplets) people are identical or non-identical twins. Twins are two people produced in the same pregnancy. They can be either identical (scientifically known as monozygotic) which means they developed from one fertilized egg (zygote) which then split and formed two embryos. Or they can can be fraternal (dizygotic) which means they developed from two separate eggs which were fertilized by two different sperm.

Identical Twins
About 33 percent of sets of twins are identical. As they developed from the same egg and sperm they share exactly the same genetic DNA information, which means they will always be either a set of boys or girls, never mixed genders. About 25 percent of identical twins are mirror images of each other meaning the left side of one matches the right side of the other.

Fraternal Twins
The majority of twins, in fact two thirds, are fraternal. As they developed from separate eggs and separate sperm, these children will be no more physically alike than other siblings born at different times. In fact half the time they are even different genders. Yet, fraternal twins of the same gender can sometimes be difficult to tell apart when they are young. Some scientists even believe that there may be another type of twin set - where the unfertilized egg splits in two and is then fertilized by different sperm. This theory may explain why some fraternal twins actually look identical.

Why Test?

The main reason is to satisfy curiosity where parents or twins themselves wish to know if they are identical or not. In fact many parents are given incorrect information about their twins by doctors at the time of birth based on a placenta examination. Unless the twins are different genders (whereby they cannot be identical), examination of the placenta or the babies with the naked eye is not very accurate. Obstetricians sometimes try to determine if twins are identical by checking the placenta membrane for thickness or how easily it can be peeled apart. This only tends to be accurate if carried out with a microscope examination - which is an expensive test - and even then is not conclusive.

Occasionally a twin DNA test is used to check suitability for a bone marrow or organ donation. Twins who donate organs to each other have fewer risks of rejection if they are identical.

Why people do NOT test is to determine if they have inherited any genetic disorders. DNA health screenings are different tests and are best taken with the advice of genetic counselors. For example, genetic testing for breast cancer is one of the most popular screenings, and specifically checks for BRCA gene mutations.

Why Are More People Testing?

In 2008, according to the American Association of Blood Banks’ (AABB) Relationship Testing Program Unit, just over 414,000 relationship tests were carried out in the U.S. Multiple births are more common now than they were in the past, primarily because of the increase in infertility treatments such as in vitro Fertilization (IVF). Additionally women planning a pregnancy after 35, which they are doing so in increasingly larger numbers, are more likely to have twins. As a woman ages and approaches perimenopause her ovaries become less responsive and the body reacts by producing more estrogen. This flood of extra hormones can over-stimulate the ovaries to produce more than one egg at a time.

When Can We Test?

Testing can be carried out on twins at any stage of life, from newborn to adults.

How To Test

Tests are available to purchase over the internet. A kit will be posted to your home, which typically includes a set of mouth swabs which are wiped inside the twins mouth. Extra swabs, in case of triplets can usually be ordered for an extra fee. The swabs are returned to the lab in envelopes provided with the kit. Results are typically posted, emailed or phoned after 5 working days and will reveal with 99 percent accuracy whether two twins are identical or not.

How Much Does It Cost?

Typically tests cost about $150. They can increase to $400 if a chain of custody needs to be established for legal reasons such as immigration.

Other Types Of Relationship Tests

Sibling DNA Tests
Paternity Tests
Y Chromosome DNA Tests
Ancestry Gene Tests
Grandparent DNA Testing

  Related Articles on Testing

For more parental advice, see the following:

Genetic Testing During Pregnancy
Paternity Test After Pregnancy

Back To Homepage: Womens Health Advice

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