Every year, about 15 million babies are born prematurely, and all sorts of complications arise as a result. Those that survive their first year of life have an increased risk of lifelong conditions. To care for those early arrivals, researchers at the Children's Hospital of Philadelphia (CHOP) have created an artificial womb that recreates the conditions needed to let their organs fully develop. Animal tests have been encouraging, with premature lambs developing normally after spending up to four weeks in the device.

On average, a healthy human baby is born at around 40 weeks of pregnancy, but any born before 37 weeks is defined as premature, or preterm. The earlier the arrival, the higher the chance of complications, and between 22 and 24 weeks is said to be the limit of viability. Any earlier and the baby has low odds of survival, but even if they do pull through, there's a 90 percent chance of lifelong disability like cerebral palsy, learning difficulties and organ problems.

"These infants have an urgent need for a bridge between the mother's womb and the outside world," says Alan Flake, leader of the study. "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."

CHOP's artificial womb is designed to carry infants from a gestational age of 23 weeks to 28 weeks. Although that's still pretty premature, by that point the fetus has crossed a safety threshold and can avoid the most debilitating consequences. The device maintains constant temperature, pressure and light, and protects the baby from infection.

The device encases the infants in a bag with artificial amniotic fluid flowing in and out. At that early stage, the baby's lungs aren't developed enough to breathe air, so there's no external pump. Instead, the baby's heart does the job, pumping blood through the umbilical cord to a low-resistance external oxygenator, which delivers oxygen and carries away carbon dioxide, a role normally performed by the mother's placenta. Vital signs and blood flow are all monitored electronically.

"Fetal lungs are designed to function in fluid, and we simulate that environment here, allowing the lungs and other organs to develop, while supplying nutrients and growth factors," says Marcus Davey, co-author of the study.

The researchers tested the system on eight premature lambs, which were physiologically equivalent to human infants of about 23 or 24 weeks old. The lambs were kept in the artificial womb for up to 28 days, and afterwards they showed normal growth, brain function, organ maturation and breathing and an increase in activity. They were also able to open their eyes and grow wool.

"This system is potentially far superior to what hospitals can currently do for a 23-week-old baby born at the cusp of viability," says Flake. "This could establish a new standard of care for this subset of extremely premature infants."

The researchers say that it could take up to a decade before these kinds of systems are widely used in hospitals. Before human trials can be conducted the team plans to further refine the artificial womb, and will need to shrink it to about a third of its current size, given how much smaller human infants are than lambs.

The research was published in the journal Nature Communications. The team describes the artificial womb in the video below.