A set of day-old conjoined twins in India who share a single heart are under careful observation as doctors try to figure out what other organs the girls might share.

The girls, who have not been named yet, weighed a combined 8 pounds, 8 ounces upon birth in the Indian state of Odisha, SWNS reported.

“This is a case of thoracopagus,” Professor Saroj Satpathy, of the Sadar Vallabhbhai Patel Post Graduate Institute for Pediatrics, which is where the girls were born, told SWNS. “The two girls have one heart as they have the same pulse and blood pressure.”

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Conjoined twins occur once in every 50,000 to 60,000 births, with about 70 percent of cases involving females. About 75 percent of conjoined twins are joined at least partially in the chest and share organs with one another, according to Children’s Hospital of Philadelphia (CHOP).

“If they have separate sets of organs, chances for surgery and survival are greater than if they share the same organs,” according to CHOP. “As a rule, shared heart conjoined twins cannot be separated.”

It was not clear if the twins’ parents, identified as Renubala and Pradeep Behera, were aware that their daughters were conjoined before their birth. Because of their shared chest, the girls are both faced inward toward each other.

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“Separation is almost impossible in such cases as there might be sharing of several other vital organs and survival chances become less,” Satpathy said.