The smallest of the Chukwu octuplets died yesterday of heart and lung failure, a week after she was born weighing 10.3oz.
Texas Children's Hospital in Houston announced that the baby, Chijindu Chidera, who was nicknamed Odera, was pronounced dead at 3.23 a.m.
She and her seven siblings had been in intensive care since her birth on December 20th as part of the world's first surviving set of octuplets. The first baby was born on December 8th.
Odera was the fifth child born to Ms Nkem Chukwu (27), a native of Nigeria, and her husband, Mr Iyke Louis Udobi.
The baby's condition began to deteriorate significantly on Saturday, when doctors moved her from a conventional ventilator to an oscillator in an effort to improve her blood oxygenation.
But her oxygen levels remained poor, and her heart began to fail. Medication and chest compressions were unsuccessful, the hospital said.
In a statement issued yesterday through the hospital, her parents said: "We are very saddened by the passing of our beloved baby, Odera. She is now safe with God in heaven, and we remain most grateful to him for having blessed our lives with hers."
Mrs Chukwu and her husband and mother visited all eight babies for the first time on Saturday night, at about the same time as Odera's condition began to deteriorate, hospital officials said.
The other seven babies were in critical condition last night. The youngest, Gorom, was recovering from abdominal surgery on Saturday to repair an intestinal perforation.
Two of the babies, Ebuka and Ikem, remained on ventilators, but four others, Chidi, Echerem, Chima and Jioke, were breathing on their own.
Their mother, who had taken fertility drugs, was in stable condition yesterday, according to St Luke's Episcopal Hospital.
Few babies as small as Odera, or her siblings, survive more than a few hours after birth. None that size has survived at Texas Children's. Dr Patti Savrick, the octuplets' paediatrician, said on Saturday that she was worried about Odera and that the girl was "literally on minute-to-minute care".
The parents yesterday thanked the doctors and hospitals for trying "to help Odera in her battle for life against what turned out to be overwhelming obstacles.
"We also want to thank people all over the world for their prayers for our family in this special time in which we are so blessed by our eight babies, but so sad for the loss of little Odera."
The largest of the babies weighed 1lb 11oz at birth.
Mrs Chukwu is expected to leave St Luke's early this week, according to her obstetrician, Dr Brian Kirshon. But because of the media attention, she was not looking forward to being discharged, said Mr Chido Nwangwu, a member of the parents' tribe in Nigeria and publisher of the Houston-based newspaper US-Africa.
"It will turn the place into a circus," he said.