FRANKFURT -- An infant who could be the youngest surviving premature baby in the world was released from a German hospital and resting at home Thursday after spending four months in an incubator.

The baby was born in early November at 21 weeks and five days into the mother's pregnancy, weighing just one pound, German news website The Local reported.

She was not initially expected to survive, as experts generally believe that babies born before the 22nd week of pregnancy will not live. Pregnancies usually last 40 weeks.

The little girl, named Frieda, now weighs more than seven pounds and was sent home Wednesday. Doctors said there was no indication that she could not be completely healthy.

There are no reports in medical literature of more premature babies having survived, although The Local said that a Canadian boy, born in 1987 at the same premature age as Frieda, survived.