It’s not always 100% clear whether or not a set of twins is identical. But thanks to advances in DNA testing technology, it’s possible to know for certain in as little as 24 hours.
Different types of twins
Broadly speaking, there are two types of twins – Fraternal and Identical.
Fraternal (non-identical) twins develop from two completely separate eggs. During the pregnancy fraternal twins will have two separate placentas. Fraternal twins can be the same or different genders, and they are no more alike than any other pair of siblings.
Identical twins develop from a single fertilised egg that splits during the first few days of a pregnancy. Depending on when exactly the split happens, the twins may share a placenta or there can be two separate placentas. This is why identifying identical twins isn’t always straightforward.
How to tell if twins are identical
Obviously, if your twins are different genders they can’t be identical. If they are the same gender but they have very different physical features (for example hair and eye colour) then it’s also safe to assume they are non-identical.
If a pair of twins shared one placenta in the womb, they must be identical.
But what if a pair of twins look very similar but they had separate placentas in the womb? It’s possible that they are identical, but it’s equally possible that they are fraternal twins that just happen to look alike. This is a dilemma that many parents of twins face. It can be difficult when strangers ask if your twins are identical and you don’t have an answer for them. It can have more serious implications as well – there are certain medical conditions that are more likely to affect identical twins.
One way to find out for certain is with a DNA test.
DNA testing for twins
A twin DNA test (or a zygosity test to use its correct name) looks at several DNA markers to determine if a pair of twins are identical or not.
Instagram influencer and mother of twins chantellechamps discovered that her twin girls were identical after ordering a home DNA twin test with next-day results. After years of uncertainty she discovered that her girls are indeed identical.
DNA testing services charge around £100 to £150 for a home DNA test. Each person taking part (e.g. the two twins) provide a mouth swab which is sent back to the lab via post.
If you’re going to order a DNA test, be sure to find a reputable testing company that is properly accredited. DNA Testing Choice is a good place to start – they are an independent review website that compares different DNA labs and collects customer reviews.
You can find more detailed info about types of twins at Twins UK.
You can read more about zygosity testing here.