Amillia Sonja Taylor, born Oct. 24 after just under 22 weeks in the womb, had been expected to be sent home Tuesday.
Barbara Moore, spokeswoman for Baptist Children's Hospital, said she did not have details on why doctors changed their minds about releasing the infant.
Doctors say Amillia is the first baby known to have survived after a gestation of fewer than 23 weeks. She was just 9½ inches long and weighed less than 10 ounces when she was delivered by Caesarean section. Full-term births come after 37 to 40 weeks.
Amillia, the first child for Eddie and Sonja Taylor of Homestead, now weighs 4½ pounds.
She has suffered respiratory and digestive problems, as well as a mild brain hemorrhage, but doctors believe the health concerns will not have major long-term effects.
"Her prognosis is excellent," said Dr. Paul Fassbach, who has cared for Amillia since her second day.
"She smiles, so everything a baby's supposed to do for her age, she's doing — which is amazing because they told me she would be developmentally delayed. She surprised us all," said the baby's mother, Sonja Taylor.
Amillia was conceived in vitro and has been in an incubator since birth. She will continue to receive a small amount of supplemental oxygen even after she goes home.