Doctors say the octuplets born in California are a feisty bunch who seem to be doing remarkably well, despite arriving nine weeks premature.
They ranged in weight from 1lb 8oz to 3lb4oz.
"We were fortunate that this patient was extremely strong, very courageous and able to handle these births," said Dr Karen E. Maples, who is chief of service for obstetrics and gynaecology at Kaiser Permanente Bellflower Medical Centre and delivered Baby number eight.
No pictures of the children were released, and at the mother's request doctors declined to reveal her name, any information about her family or whether she took fertility drugs before becoming pregnant, though outside experts said it is almost certain she did.
The chances of delivering eight babies naturally are "unbelievably rare," said Dr Richard Paulson, director of the fertility programme at the University of Southern California.
The babies have not been named yet, and the staff assigned them letters A through H in the meantime. They were expected to remain in hospital for several weeks and could face serious developmental problems later on because of their small size.
"They are doing amazingly well at this time," said Dr Mandhir Gupta, a neonatologist who was part of the team of 46 doctors, nurses and others who took part in the cesarean section delivery.
But he added: "I won't be able to comment on chances of survival because we've never had eight babies born at 30 weeks before."