A premature baby that doctors say is the first to survive after a gestation of fewer than 23 weeks will be staying in a Florida hospital a little longer.

Amillia Sonja Taylor had been scheduled to leave for home on Tuesday, but doctors decided she should remain in their care a few extra days as a precaution.

A spokeswoman for Baptist Children's Hospital did not have details on why doctors changed their minds about releasing the infant.

Amillia weighed just 284 grams -- or less than 10 ounces -- when she was born Oct. 24, 2006. She measured just 9 1/2 inches long -- a little longer than a ballpoint pen.

She was delivered by Caesarean section at 21 weeks and six days after conception, after attempts to delay a premature delivery failed. The exact date of her conception was known because she was conceived by in vitro fertilization.

Dr. William Smalling, the neonatologist at Baptist Children's Hospital in Kendall, Florida, where Amillia was born, said Monday his team was not optimistic about Amillia's prospects at birth.

"But she proved us all wrong," he told reporters Monday.

"She's truly a miracle baby."

The American Association of Pediatrics says babies born at less than 23 weeks of age are not considered viable. The mortality rate for such infants is 70 per cent, according to the National Institutes of Health.

Amillia is now thriving and weighs two kilograms (4 1/2 pounds) and is about 25 inches long.

Although she has experienced respiratory problems, a very mild brain hemorrhage and some digestive problems, none of the health concerns are expected to pose long-term problems, her doctors said.

"We can deal with lungs and things like that but, of course, the brain is the most important," Dr. Paul Fassbach said. "But her prognosis is excellent."

Amillia is the first child for Eddie and Sonja Taylor, who say they are delighted with her progress.

"She smiles, so everything a baby is supposed to do for her age she is doing, which is amazing because they told me that she would be developmentally late," her mother Sonja told reporters.

"It was hard to imagine she would get this far. But now she is beginning to look like a real baby. Even though she's only four pounds, she looks plump to me."

Amillia has been in an incubator since birth and has been receiving oxygen. She will continue getting a small amount of oxygen, and her breathing will be monitored once she leaves hospital.

"She's going to be in a normal crib, she's going to have normal feedings, she's taking all her feedings from a bottle," Smalling said.