An artificial womb which successfully nurtured premature lambs is bringing hope it could eventually be used as a vital lifeline for human babies.
Researchers from the Children's Hospital of Philadelphia recreated a womb in a bag and grew foetal lambs in an amniotic fluid-filled, temperature-controlled, near-sterile environment.
Their hearts pumped blood through their umbilical cord into a gas exchange machine outside of the bag.
While similar systems had been tried before - the pumpless versions achieved a maximum of 60 hours and caused some brain damage - the new system was able to be used for up to 28 days.
The lambs showed normal breathing and swallowing behaviours, were able to open their eyes, grew wool, were active and showed normal growth and neurological function as well as organ development.
It could give extremely premature babies a few more vital weeks to develop their lungs and other organs.
"Our system could prevent the severe morbidity suffered by extremely premature infants by potentially offering a medical technology that does not currently exist," study leader and director of the hospital's Center for Fetal Research Dr Alan Flake says.
The lambs were chosen as the study's subjects partly because their prenatal lung development is similar to humans.
The six lambs tested using the system, which has undergone four iterations in three years, were the equivalent of 23- to 24-week-old human baby.
The system will be refined further, partly to downsize it for infants which are around one-third the size of the lambs used in the study.
Dr Flake says if the results can show the same results for premature babies, it could significantly improve the poor survival rates and give them a chance at a normal life.
Critically pre-term babies born around 22 to 23 weeks weigh less than 600gm and have a 30 to 50 percent survival rate.
Even if they do survive, Dr Flake says there's a 90 percent chance of morbidity from chronic lung disease or other complications from organ maturity. Those who do survive can face lifelong disability.
They aim to nurture babies from 23 weeks to 28 weeks where the risks to health are lessened.
"These infants have an urgent need for a bridge between the mother's womb and the outside world.
"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 says.
If successful, Dr Flake says they could be in use by humans in a decade; aside from the obvious medical benefits, he says it could also save the US health system $4b a year in medical costs.
"This system is potentially far superior to what hospitals can currently do for a 23-week-old baby born at the cusp of viability."
However, Dr Flake says they won't be extending the procedure to infants younger than 23 weeks because the risks are "unacceptably high".
The study was published in Nature Communications.