The infant, who was identified only as Nazia, died late Tuesday after a two-hour operation earlier that day at The Children's Hospital at Pakistan Institute of Medical Science in the capital, Islamabad, said Zaheer Abbasi, head of pediatric surgery at the hospital.
Abbasi, the chief doctor who led the operation, said the case was the first he was aware of in Pakistan of fetus-in-fetu, where a fetus has grown inside another in the womb.
"She was very weak in fact because the surgery was a major undertaking and her system couldn't take it," Abbasi said.
Abbasi described the situation as a case of triplets, with two growing inside another. Surgeons removed the two partially grown fetuses, totaling about two pounds that had died at about 4 months.
The infant girl came from Abbotabad, about 30 miles north of Islamabad. She is the fifth child of a woman in her 30s, who was at the hospital to be with her daughter. Her father works in the Arabian Gulf.
Other fetus-in-fetu cases have been reported elsewhere in the world. A report in a June 2000 issue of the U.S. journal Pediatrics called such occurrences rare and estimated their rate at about one per 500,000 births.