Researchers have kept premature lambs alive for several weeks using a 'biobag' designed to mimic the conditions of a womb.
The artificial womb consists of a plastic bag filled with fluid that provides a temperature-controlled, near-sterile environment. The premature lambs breathed amniotic fluid as they normally would in the womb, and their hearts pumped blood through their umbilical cord into a gas exchange machine outside the bag, which acts like the placenta.
'Our system could prevent the severe morbidity suffered by extremely premature infants by potentially offering a medical technology that does not currently exist,' said study leader Dr Ian Flake, a fetal surgeon and director of the Center for Fetal Research at The Children's Hospital of Philadelphia (CHOP), USA.
'What they've got is a system where the fetus is really existing very much as it would in the mother's womb. The fetus knows what to do,' maternal-fetal medicine specialist Professor Anna David of University College London, who was not involved in the research, told Science magazine.
Researchers tested the system on eight premature lambs which had been born after about 110 days gestation, which is the equivalent of approximately 23 weeks in humans. They showed that the lambs could survive and grow for up to a further four weeks.
In the UK, around 60,000 babies are born prematurely each year. With new techniques they can be kept alive from increasingly early age; however, babies born before 28 weeks have a higher risk of death or of morbidity, including chronic lung disease and other organ complications.
'The challenging age that we are trying to offset is that 23- to 24-week baby who is faced with such a challenge of adapting to life outside of the uterus on dry land, breathing air when they are not supposed to be there yet,' Dr Emily Partridge of CHOP and first author of the study told the BBC.
'These infants have an urgent need for a bridge between the mother's womb and the outside world,' said Dr Flake. 'If we can develop an extra-uterine system to support growth and organ maturation for only a few weeks, we can dramatically improve outcomes for extremely premature babies.'
Dr Flake stresses that the team does not aim to extend viability to an earlier period than the current mark of 23 weeks. Before that point, limitations of physical size and physiological functioning would impose unacceptably high risks.
Colin Duncan, professor of reproductive medicine and science at the University of Edinburgh, who was not involved in the research, agrees. 'This research isn't about replacing the womb in the first half of pregnancy. It is about the development of new ways of treating extremely premature babies,' he told the BBC.