It’s estimated that 12% of human pregnancies begin as multiple pregnancies, but less than 2% end that way. What happens to the other embryo?

Recall that identical twins occur when one egg splits into two and results in two embryos. But sometimes one of the embryos simply vanishes, leaving only one to develop to term. So how would you know if you started out with a twin that disappeared?

A new study suggests there may be a way to find out. This study, published Tuesday, Sept. 28, 2021, in the journal Nature Communications, explains how researchers focused on what is called epigenetic modifications found in twin DNA. “Epigenetic” refers to factors that can turn genes “on” or “off” without changing the DNA sequence. For example, small molecules called methyl groups can stick to specific genes and keep the cell from reading those genes. Thus the genes are deactivated.

According to this new study, the DNA of identical twins has a characteristic pattern of sticky methyl groups. This pattern covers 834 genes and can be used to differentiate identical twins from both fraternal twins and non-twins. The research team developed a computer algorithm that can identify an identical twin based solely on the location of methyl groups across their DNA. 

So this tool should also be able to spot someone who’d had a vanished twin. That’s the theory, although the study didn’t go there.

Of course, this line of research is useful in other ways, too, like why do cells split to form multiple embryos in the first place?

Anyway,the complete discussion of this research can be found in Did You Share the Womb With a ‘Vanishing Twin’? The Answer May Be Written in Your DNA by Nicoletta Lanese (https://www.livescience.com/identical-twins-unique-epigenetic-signature? ).