Every year, millions of babies are born before they are fully developed. Many of them die because they are not yet able to survive outside their mother.

An estimated one million children worldwide die each year from problems resulting from being born too early, a condition called preterm birth.

Now, researchers say they have developed an artificial womb that kept alive preterm baby sheep. They say the artificial womb acts like a uterus – the female organ where sheep, babies and other creatures develop before they are born.

The findings were published in the journal Nature Communications.

Preterm babies are born before 37 weeks of gestation, or time spent in a mother's womb. Most medical experts agree that a baby can survive outside the mother's body after 24 weeks. But one study showed that babies can survive as early as 22 weeks if treated.

FILE: A premature baby at Children's Hospital in Philadelphia, PA. (Credit Children's Hospital of Philadelphia)

When babies are preterm or premature, they are called ‘preemies'. At 22 to 23 weeks of gestation, an infant weighs less than 600 grams. The lungs and other organs are not yet fully developed. This causes breathing problems, which can lead to death. If such babies live, survivors may have physical disabilities for the rest of their lives.

Doctors place preemies in a temperature-controlled box called an incubator. There, the baby is connected to special equipment that pushes oxygen into the lungs, helping the child to breathe.

American researchers have developed technology that may help these youngest babies survive. The researchers created an artificial womb, or man-made uterus. They have had baby lambs living and growing inside the artificial womb for up to four weeks.

The researchers are working at the Children's Hospital of Philadelphia in Pennsylvania.

The hospital has been testing the artificial womb, which officials are calling a "biobag."

Alan W. Flake led the study. He said that if researchers can develop a system to support growth and organ development for only a few weeks outside the mother, "we can dramatically improve outcomes for extremely premature babies." Their goal is to help infants from 23 weeks to 28 weeks.

When a baby is growing inside a normal uterus, it is surrounded by amniotic fluid. The biobag is filled with fluid similar to a mother's amniotic fluid. The researchers say being in this biobag can give a baby more time to develop normally. This may be true even if the child is born as early as 23 to 27 weeks.

In the study, baby lambs using the biobags were able to breathe amniotic fluid as they normally would do in the womb.

Lauran Neergaard is a medical writer for the Associated Press. She explains what the Children's Hospital researchers designed.

"So, these researchers decided to go back to Mother Nature and mimic a mom's uterus with a fluid-filled container that preemies could be put into and take in amniotic fluid -- a substitute for amniotic fluid -- the way that they would in the womb."

When a baby is inside the mother's body, the two are connected through an umbilical cord. This long, narrow tube provides oxygen to the baby and takes away carbon dioxide. In the artificial womb, a machine connected to the lamb's umbilical cord does the same job: it provides oxygen and takes away the carbon dioxide. The heart pumps blood through the cord to a gas exchange machine outside the bag.

But this technology is very new. So it is a long road from this experiment to helping the estimated 15 million preterm babies born every year.

Lauran Neergaard says the baby lambs grew in the artificial womb.

"Now, there are no long-term data on these animals, but what they did find is they appeared to grow normally. They were able to watch them over this period grow wool, even."

The researchers examined the lambs' organs later. Neergaard reported that the organs were similar to those from lambs of the same age that had grown in a natural womb.

The hope is that these biobags may provide a ‘safe space' for premature babies to develop in a more natural way -- even if they are no longer able to grow inside their mothers.

Human testing is still three to five years away. But already, researchers are talking to U.S. officials about making the biobags available to hospitals.

And I'm Pete Musto.

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Words in This Story

artificial womb – n. a man-made container made to act like a human uterus—the female organ in which babies grow

gestation – n. the time when a person or animal is developing inside its mother before it is born

outcome – n. something that happens as a result of an activity or process

incubator – n. a piece of equipment in which very weak or sick babies are placed for special care and protection after their birth

amniotic fluid – n. the fluid in which the embryo or fetus is suspended within the uterus

Mother Nature – n. used to refer to the natural world as if it were a woman

mimic – v. to copy someone or someone's behavior or speech

umbilical cord – n. a long, narrow tube that provides oxygen to the baby in the uterus and takes away carbon dioxide