Only DNA Testing Can Tell. Twins- Identical? Fraternal?

Approximately one in every eighty births results in the delivery of twins. Although the misconception persists, the number of placentas cannot determine if same-sex twins are fraternal or identical - only DNA testing can. One third of identical twins have two placentas and more than 40% of fraternal twins have a single, fused placenta.

DNA testing to determine if twins are identical or fraternal is called twin zygosity testing. Twins that are dizygotic or fraternal are the result of two different sperm fertilizing two different eggs and share only the same amount of DNA as full siblings born at different times.

Monozygotic or identical twins are the result of one egg fertilized by a single sperm that splits in two and have identical DNA. Most twins have zygosity testing performed simply to satisfycuriosity. However, knowing if twins are identical or fraternal can be a safeguard for possible future medical emergencies—identical twins are perfect organ and tissue donors for one another.

Although identical twins often look so much alike that we have difficulty recognizing one from the other, many do notbecause their genes express themselves in different ways. Alternatively, fraternal twins can appear to be identical when they are not, like the famous Olsen twins. If you are a twin or know a twin that has ever wondered, DNA testing is the only way to answer the question with certainty.