Photo/IllutrationA baby boy, born at 268 grams, on his fifth day at Keio University Hospital in Tokyo (Provided by Keio University Hospital)

A premature baby that weighed just 268 grams at birth finally headed home after six months of extensive hospital care.

The infant, born in August, was sent home Feb. 20 from Keio University Hospital in Tokyo, making him the world’s lightest-ever newborn boy to be discharged in good health.

The boy has grown to 3,238 grams with no complications after undergoing nutrition management and other care, the hospital said Feb. 26.

“To be honest, I even didn’t know whether my baby could survive,” said the 29-year-old mother of the infant. “I’m just so happy.”

The baby was urgently delivered at 24 weeks by Caesarean section, as his slow weight gain put him at high risk of death in his mother’s womb.

After receiving a course of drip intravenous injections and other treatments, the thriving infant became able to drink milk on his own.

The survival rate for babies born weighing under 300 grams is low, the hospital said. It is more difficult to save boys than girls apparently because their lungs develop more slowly, it added.

Only four boys among 23 prematurely born babies worldwide and weighing under 300 grams have survived to discharge thus far, according to a University of Iowa database.