Faux womb keeps preemie lambs alive

Premature babies may one day continue developing in an artificial womb, new work with sheep suggests.

A fluid-filled bag that mimics the womb kept premature lambs alive and developing normally for four weeks, researchers report April 25 in Nature Communications. Lambs at a gestational age equivalent to that of a 23- or 24-week-old human fetus had normal lung and brain development after a month in the artificial womb, the researchers discovered. A similar device might be ready for use in premature human babies in three to five years if additional animal tests pan out, study coauthor Alan Flake estimates.

But this is not the science fiction scenario of Brave New World, in which humans were grown entirely in tanks, says Flake, a pediatric and fetal surgeon at the Children’s Hospital of Philadelphia. “I don’t view this as something that’s going to replace mothers.” Technical and biological hurdles would prevent doctors from using an artificial womb to rescue premature babies younger than about 23 weeks, he says.

Researchers have been trying for 60 years to make an artificial womb or artificial placenta, says George Mychaliska, a pediatric and fetal surgeon at the University of Michigan Medical School in Ann Arbor. His own group has been working on an artificial placenta, or what he calls an “extra-corporeal life-support” system for premature babies for a decade. “One month is very impressive, and the data behind that is strong,” Mychaliska says, but adds that what works for lambs might not work as well for human babies.

In the United States, thousands of babies each year are born extremely premature, before 28 weeks of pregnancy. Of those born at the edge of viability, at 23 weeks of gestation, up to about 70 percent die; many of the survivors have lung and other health problems partly caused by efforts to keep them alive. Putting premature babies on ventilators to get oxygen into their bodies has mixed results, Mychaliska says. “The same treatment that is potentially saving their lives is also damaging their lungs.”

Flake and colleagues’ initial efforts to make an artificial womb — including submerging lambs in fluid in a tank — failed. Infection soon set in, killing the animals. This time, the researchers tried to mimic more closely what happens during normal pregnancy. In the new system, a lamb is surgically delivered via cesarean section and placed in a sterile bag filled with an electrolyte fluid. Because the bag is closed, the risk of infection is reduced. Tubes carrying oxygenated blood plug into the lamb’s umbilical cord, and the beating of the fetus’s heart pumps the blood at volumes and pressure comparable to what is normally delivered by the placenta. Other groups have put tubes in the neck and used an external pump to circulate the blood, which may put too much pressure on fetal hearts, causing heart failure, Flake says.

Like a real womb, the artificial one also bathes lambs in the fluid needed for proper lung development. Flake’s team prevents the lambs from taking a breath because even a little air might harm lung development.

Premature babies would have to be delivered surgically and placed immediately into the fluid incubator. That would rule out about 50 percent of extremely premature babies because they are born vaginally, Flake says.

Flake’s version of the device may not be feasible for human babies for several technical reasons, too, Mychaliska says. One barrier is that the system requires a delicate fetal surgery to connect the umbilical cord to the incubator while the baby is still attached to the mother. Few hospitals are equipped to perform such an operation, he says. 

Flake acknowledges that several kinks must still be worked out before the artificial womb can be tested on human babies. “We have a lot to learn in terms of its capabilities and its safety,” he says, but his group may soon be ready to begin human clinical trials. “We honestly think it could be as early as two to three years from now — and certainly within five years — that we’ll be applying it to humans.”