In a super rare occurrence, conjoined twins born in Indonesia have four arms, three legs and shared genitalia. Such twins are scientifically known as ischiopagus tripus and is one in a two million phenomenon. Just a handful of such conjoined twins, also referred to as ‘spider twins’, have been recorded – the case of Indonesian boys has been published in American Journal of Case Reports. The twins were born in 2018, but the case was published in the journal this week.

“The rarity of ischiopagus tripus conjoined twins complicates the surgical separation, owing to the lack of cases and high complexity,” the authors wrote in the American Journal of Case Reports.

They are defined as those who are connected by the lower half of their body instead of the upper torso.

In over 60 per cent of such cases, one of the twins dies or is stillborn. But these toddlers survived all the odds. The brothers, however, had to lie flat for their first three years as their unique body structure prevented them from sitting up.

The case report says that surgeons amputated their third leg – which is often two fused legs – and stabilised their hips and legs so the brothers could sit upright independently.

A follow-up appointment three months after the surgery revealed that the twins didn’t suffer any complications.

The twins are not separated, and it is not known if the doctors will attempt such a complicated surgery.

Still, doctors believe that the case highlights that “there is still room for surgical correction to be performed” in cases where separation is not possible.

A birth like this takes place when the embryo only partially separates to form two people due to a congenital birth defect, as per Mayo Clinic.

While the babies develop from this embryo, they remain physically joined, most “often at the chest, abdomen or pelvis”.