Have you ever wondered if your twins are identical?

DNA Testing is the only way to be certain.

With approximately one in every sixty births resulting in the delivery of twins, twin testing has become very popular. Twins are either dizygotic (commonly referred to as fraternal) or monozygotic (identical). Dizygotic twins are the result of two different eggs being fertilized by two separate sperm and resulting in two completely distinct and separate pregnancies in the womb at the same time. Monozygotic twins are the result of one egg fertilized by a single sperm. The fetus literally splits in two around the time that pregnancy is implanting in the womb (between the fourth and twelfth day of development). Monozygotic twinning accounts for approximately 30% of twin births while the remaining 70% of twins are dizygotic. Many parents are given misinformation at the time of their twins’ birth based on an incomplete or erroneous examination of the placenta. Unless the twins are of different sexes (with extremely rare exceptions) or inside a single amniotic sac, examining the babies or the placenta with the naked eye is not very helpful.

The number of placentas does not predict zygosity. One third of monozygotic twins have two placentas and 42% of dizygotic twins have a single, fused placenta. Many obstetricians try to determine the zygosity based on how thick or thin the membrane between the two bags of water is, or by how easily it can be peeled apart. This is only accurate if a microscopic examination is done after special processing of the tissues. This examination is expensive and often inconclusive.

Affiliated Genetics has performed more zygosity tests for multiples than any other laboratory offering this service. Since our inception in 1994, we have performed zygosity tests for many university studies, private genetics labs, pediatricians and the public. DNA twin zygosity testing can be performed at any age–newborns to adults. A sample collection kit is mailed to your home. The sample collection is easy and non-intrusive. A sponge tipped swab is used to collect the cheek cells and saliva from the inside of the mouth. Designated areas on a specially treated card are then saturated. The card will hold a small number of cheek cells from which we can obtain DNA. The DNA sample is then analyzed using well-characterized DNA markers. A letter of results signed by the molecular geneticist is usually mailed within 7 working days from the date our laboratory receives the samples. In the unlikely event the amount of DNA from the first sample is insufficient, a second kit will be sent at no extra charge.

The typical reason to have a zygosity test performed is simply to satisfy curiosity. Many use this as a fun family activity or science project. There are however, medical reasons for zygosity testing. Because monozygotic twins have the same genetic code, they may be able to help each other in extreme medical circumstances. In the event of organ transplantation, identical twins would have the best chance for organ acceptance. Usually, identical twins have the same blood type so they could share blood in emergencies.

Our testing is affordable, reliable, and highly accurate. Our cheek swab DNA testing gives 99% or greater accuracy, which is the same accuracy as a blood DNA test. All results are kept completely confidential and all samples are destroyed after 30 days. Our physician who is board certified in OB/GYN, Perinatology, Clinical Genetics, and Molecular Genetics reports each case.  The test fee includes materials and analysis for two twins.  Additional fees apply for additional multiples.