The babies are being attended round-the-clock by a team of doctors and nurses in the intensive care unit of St Luke's Episcopal Hospital in Houston, Texas. Hospital authorties say they are all in a critical but stable condition.

Five girls and two boys were born on Sunday after the first child, a girl, was delivered on 8 December.

The BBC's Emma Simpson on the octuplets

Some of the babies weigh as little as 11oz, but hospital authorities said they had an 85% chance of survival.

The eldest child is now breathing naturally, but the remaining babies require the assistance of a ventilator. Two of them are receiving oxygen ranging from 35% to 100%.

All eight babies are receiving intravenous fluids, and are beig kept sleepy and quiet under a plastic warming bed. They have also received treatment to guard against lung disease.

The babies' mother Nkem Chukwu was in a stable condition following surgery early on Monday morning to control bleeding following the births.

Mrs Chukwu gave birth to seven of the children by Caesarean section on Sunday morning at St Luke's - the largest children's hospital in the USA.

Her first child was born two weeks earlier without the help of surgery.

Dr Kirshon: It's so unusual that the babies are able to survive

Until then, doctors had been unsure how many foetuses Ms Chukwu was carrying, said Brian Kirshon, one of three doctors who delivered the children.

The girl born on 8 December was 12 weeks premature; the others were delivered by Caesarian section 10 weeks early.

The babies' weight ranges from 11oz to 1lb,11oz.

'Hanging in there'

Dr Weisman: "Anywhere along the way they can have a catastrophic event"

The hospital's chief neonatal specialist, Leonard Weisman, said potential lung and heart problems were the immediate worries. Metabolic problems and infections would also be a danger.

Dr Patti Savrick, a paediatrician at the hospital, said the babies were as well as could be expected. "They're hanging in there."

It will be at least two months before the babies can be released from hospital.

The children are the first for Ms Chukwu and her husband, Ike, who live in Houston and both originally come from Nigeria. The couple had long tried to have children, before resorting to fertility drugs, Dr Kirshon said.

Ms Chukwu miscarried triplets earlier in 1998 while taking the drugs.

"The recent loss ... made her cautious about this pregnancy," the doctor said.

Model patient

Ms Chukwu entered hospital in early October and had been confined to bed for six weeks. The doctors said she had been a model patient.

To keep pressure off her lower body for the past two or three weeks, Ms Chukwu's bed was put at an extreme incline with her head downwards, Dr Kirshon said.

Sheryl Stavins of St Luke's hospital on the octuplets

"I think she is remarkable in that she was able to tolerate extreme conditions, to lie upside down in that degree of discomfort and that degree of immobility," he added.

Ms Chukwu had also offered to forego food if it would make more room for the babies in the womb.

Dr Kirshon, who specialises in high-risk pregnancies, said at least 25 people were involved in the deliveries, ferrying the babies in assembly-line fashion as they were removed from the womb.

Multiple births

According to the Guinness Book of World Records, the largest multiple birth was nine babies in Sydney, Australia, in 1971. All the children died.

Three other octuplet births have been recorded in the past 13 years, but in each case, some of the babies died.

In 1985, a 25-year-old Turkish woman who had been taking fertility drugs gave birth to octuplets, but six died within 12 hours. The remaining two died within three days.

Rosario Clavijo, 31, from Huelva in Spain, became pregnant after using fertility drugs and gave birth in December 1996 to six healthy babies. Two children died.

In August 1996, a 32-year-old British woman, Mandy Allwood, conceived eight foetuses and rejected medical advice to abort some of them. All of them died.