The team at Tokyo's Juntendo University reckon that in 10 years' time, the same technology could be used to improve the survival of premature babies, and to provide an alternative womb in the case of mothers bearing multiple foetuses.
The experiments have been in progress for six years, but the scientists have only now decided to release more information.
Although some have expressed fears that it could lead to the scenario described by Aldous Huxley in Brave New World, where millions of children are bred and grow in sterile incubators, the team emphasised that their system cannot replace the crucial stage in which the fertilised egg grows through the embryo stage.
Rather, it could eventually help premature babies, who are frequently unable to get enough oxygen into their blood because their lungs have not developed fully. Similarly, in multiple pregnancies - such as that of Mandy Allwood, who last year lost eight foetuses - it would be possible to make space in the womb by removing some of the developing embryos.
Lord Robert Winston, one of Britain's foremost fertility experts, from Hammersmith Hospital, London, said: "The current problem is that babies that are born prematurely are too immature to breathe and fend for themselves. A technique like this may well save a number of babies that would otherwise die."
The team, led by Yoshinori Kuwabara, professor of obstetrics at Juntendo Uniiversity, carried out a number of trials. They removed a goat embryo from its mother 17 weeks into pregnancy and then placed it in an open- topped transparent acrylic tank, filled with liquid at blood temperature. This simulated the amniotic fluid in a real womb. The placenta was replaced by a machine which pumped oxygen and nutrients into the embryo's blood.
A number of kids have been born from the tank. The scientists announced their achievement today having kept one hand-reared goat, Kanna - meaning Flower - alive for six years.
Professor Kuwabara said: "This system should be used on behalf of the mother who cannot keep the foetus in her uterus. If I have time and money for experiments, maybe within 10 years we will have made the move from animal to humans."
The Japanese team was advised by British doctors, but the experiment could not be carried out here because it would have breached ethical guidelines.