About one in eight people had a twin embryo that didn’t survive to term, and in future there may be a simple cheek swab test that can reveal if you are in this group.

Jenny van Dongen at VU Amsterdam in the Netherlands and her colleagues have found that identical twins carry a characteristic pattern of alterations to their DNA, known as epigenetic changes, that isn’t seen in people who didn’t have twin embryos. These variations happen in early pregnancy and last into adulthood.

Epigenetic changes are chemical modifications of DNA that help keep genes turned on or off. In early pregnancy, embryos undergo swathes of such alterations to programme different cells to become the various parts of the body.

Van Dongen wondered if this process would work differently in multiple pregnancies. About one in 100 births globally are of twins, but studies have suggested that 12 per cent of people could have had a twin embryo at some point during pregnancy that didn’t survive. Although this may be referred to as vanishing twin syndrome, there can be visible remains.