Noah Kipfmiller, now aged six months, is doing well after the groundbreaking operation, carried out when he was a 23-week-old foetus.
The success of the treatment will bring hope to other parents whose babies are shown to have defects duringscreening early in pregnancy.
The world's first operation on a foetus was carried out at Guy's Hospital in London five years ago, when surgeons used a fine needle to clear a blockage in the heart. A handful of similar operations has been carried out in Britain since but much of the experimental work is now conducted in America.
The operation on Noah was much more complex, involving closing the spine in the middle of the back where the skin and bone had failed to form, leaving the spinal cord exposed. Spina bifida is a congenital defect that varies in severity and children born with it may be paralysed and suffer hydrocephalus (water on the brain), which can cause brain damage.
Professor Scott Adzick, the surgeon who led the research team at the Children's Hospital, Philadelphia, said the child's mother, aged 27, and father had refused the offer of an abortion. "They were going to take care of the child either way so they decided to give the baby the best possible chance," he said.
The operation involved lifting the mother's womb through an incision in her abdomen, and opening it so that the baby's back was exposed. Skin taken from its back was grafted over the exposed spinal cord to protect it and a drainage tube fitted to remove fluid accumulating in the skull. The surgeons then replaced the amniotic fluid with a solution, put the womb back and sewed up the woman's abdomen. The baby was born seven weeks later by Caesarean section.
It is still too early to gauge whether the boy will have a limp but he has been spared the worst effects of the condition. He has a slight abnormality in his left foot and a right club foot, which can be treated.
Professor Adzick, who describes the case in The Lancet, said: "He is a very nice baby. The orthopaedic specialists are looking after him and he has an exercise programme. We are pleased with the way he is doing."
Professor Adzick has previously operated on a foetus who was found to have a benign tumour growing in his chest that threatened to obstruct the normal development of his lungs.
In addition to correcting birth defects that would cause paralysis or death if left until after birth, foetal surgery offers other potential benefits. Incisions heal without scarring and researchers believe transplants carried out while the immune system is still immature may overcome the problem of rejection.
However, the developments raise acute ethical difficulties. Transplants would involve using organs from aborted foetuses, which might have to be kept alive until the organs were at the right stage of development to make them suitable for transplant. Public disquiet at the prospect of "farmed foetuses" makes the introduction of such transplants unlikely.Reuse content