Pregnancy is usually an exciting time for expectant parents, however, it’s not without its dangers. One-in-three pregnancies end in a miscarriage during the first trimester and, unfortunately, various factors can lead to abnormalities even when a baby is carried to term.

One of the rarest fetal abnormalities is a parasitic twin. This happens when one identical twin stops developing properly in the womb, causing problems for its healthy sibling by failing to detach from their body. The odds of having a parasitic twin are one in a million.

While cases of parasitic twins are rare, thanks to developments in modern medicine, this condition does not necessarily equate to a death sentence for the healthy baby – however, because the parasitic twin has not developed properly, their death is inevitable.

The only reason parasitic twins are able to survive is because they live off of their healthy twin’s bodily functions.

If the twins aren’t separated, this can put a deadly amount of strain on the healthy twin. Although there have been documented cases of people carrying around their parasitic twins well into adulthood without knowing because they died in the womb.

The twins in this case were separated by surgeons at the King Abdullah Specialised Children’s Hospital in the Saudi capital Riyadh. Their parents, whose names are not known, had called their healthy twin, a boy, Haneen, and named his parasitic sister Farah.