Melinda Star Guido was born last August, 16 weeks early, weighing only 9.5 ounces (270 grammes)- less than a can of soda or the same as two iPhones - and has spent nearly five months in a neonatal intensive care unit.
She is the third smallest baby to survive, according to Global Birth Registry figures cited by LA County health officials.
Dr Rangasamy Ramanathan, neonatology chief at the LA County-USC Medical Center, said he wasn't initially sure if Melinda was going to survive beyond a few days.
"This doesn't happen every day. In my 30 years here, ... this is the first time it ever happened that we were able to discharge a baby who weighed less than 400 grams, or 300 grams," he said.
"We have reached a milestone by being able to see Melinda go home," he added "We are hopeful to see many more milestones accomplished in Melinda's development as we follow her care over the next six years." (AFP)