Speaking publicly for the first time since the birth, Mr Udobi thanked God for what he called "a great gift".

Doctors now say they are optimistic at the prospect of survival for the octuplets, who were born in Houston, Texas.

Dr Weisman: Looking for steady progress

The head of the neo-natal unit of the St Luke's Episcopal Hospital, Leonard Weisman, said the babies' breathing had improved and all but the weakest one were expected to be taken off ventilators by the weekend. The eldest baby is already breathing unaided.

The six girls and two boys have now been given traditional Ibo names from the south-east of Nigeria, where their father was born. The smallest and weakest baby, a girl, has been given a name meaning "God has my life."

They remain in a critical condition, but doctors say progress will inevitably be slow.

The babies' mother, Nkem Chukwu, is continuing to recover after undergoing surgery to stop bleeding following the birth.

"With babies this premature, you don't want significant changes - you want time," Dr Weisman siad.

"You want time for their lungs and hearts to develop and time for their bodies to get stronger. The first few days are critical, and we continue to look for small, steady progress."

The eldest baby is being fed formula. The other seven babies are receiving intravenous nutrition, a combination of proteins, fats, electrolytes, glucose, vitamins and minerals.

All eight are responsive to sound and light, but remain undisturbed and quiet on warming beds.

The family issued a statement saying: "Our family is very excited and grateful to God. We are very appreciative of the worldwide support over the past few days, particularly the prayers and spiritual connection at this special time of the year.

"As you can imagine, while we are overwhelmed, all of our concerns at this time are Nkem and the babies."

Caesarian section

The BBC's Geeta Guru-Murthy: "Doctors are still concerned about the health of one baby girl"

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

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

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 (300g) to 1lb 11oz (750g).

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

The children are the first for Ms Chukwu and Mr Udobi, who live in Houston and both originally come from Nigeria. The couple had long tried to have children, before using to fertility drugs.

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.