How to build an artificial womb

THESE days, in rich countries, premature birth is the main cause of infant mortality. A baby born at 23 weeks—just over half way through a normal pregnancy—has a fighting chance of survival. But underdeveloped lungs struggle to cope with breathing air. External pumps used to circulate blood impose potentially fatal stresses on tiny hearts. Those that do pull through are often left with lifelong problems that range from brain damage to blindness. In a paper just published in Nature Communications, a team of doctors at the Children’s Hospital of Philadelphia, led by Alan Flake, describe an artificial womb that, they hope, could improve things dramatically, boosting the survival rate of the most premature babies while reducing the chance of lasting disabilities.

The device, which looks a bit like a high-tech jiffy bag, is designed to mimic a real womb as closely as possible (see picture above, of a fetus after 28 days in the artificial womb). The fetus—a lamb in the team’s trials—is surrounded in a substitute for the amniotic fluid that keeps the animal’s lungs filled with liquid in a real uterus. Once the fetus is placed inside the bag it is sealed, to prevent germs entering. The cannulas which carry blood away to be recharged with oxygen and nutrients are inserted into the animal’s umbilical cord, and the tubing in the oxygen-exchange system is short, which lets the researchers dispense with pumps entirely. Instead, they rely on the animal’s own heart to push blood around the system.