Artificial womb system EXTEND shows promise for extremely premature babies

Scientists in the United States continue to make progress on an experimental artificial womb system known as EXTEND, a technology designed to support the development of extremely premature babies by mimicking conditions inside the human uterus.

EXTEND — short for Extra-uterine Environment for Newborn Development — was developed by researchers at the Children’s Hospital of Philadelphia (CHOP) in collaboration with the University of Pennsylvania. The system is intended for babies born at the very edge of viability, typically around 22 to 25 weeks of gestation, when survival rates remain low and the risk of long-term disability is high.

Rather than functioning like an incubator, EXTEND aims to recreate the womb itself. The premature infant is placed inside a sealed, fluid-filled bag containing a synthetic amniotic fluid. The baby’s lungs are not used for breathing; instead, oxygen and carbon dioxide are exchanged through an external circuit connected to the umbilical cord, similar to how a placenta works during pregnancy.

How EXTEND works

The system allows the foetus to:

• Remain submerged in a sterile, temperature-controlled fluid

• Avoid mechanical ventilation, which can damage immature lungs

• Continue natural development of the brain, lungs and other organs
  

Blood is circulated through a low-resistance oxygenator using the infant’s own heart, without the need for an external pump. Researchers say this approach reduces stress on fragile organs compared with conventional neonatal intensive care.

Research results so far

EXTEND has not yet been used in humans, but results in animal studies have been significant. In landmark experiments published in Nature Communications in 2017, researchers successfully supported premature lambs — equivalent in developmental stage to a 23- to 24-week human foetus — for up to four weeks. The lambs showed normal growth of the lungs, brain and other organs.

Subsequent studies refined the technology, improving infection control, circulation stability and neurological outcomes. Researchers stress that these studies were designed to demonstrate feasibility and safety rather than readiness for clinical use.

When could it be used in babies?

CHOP researchers have repeatedly emphasised that EXTEND is not intended to replace pregnancy or be used from conception. Instead, it would act as a bridge between the womb and neonatal care for babies born far too early to survive with current treatments.

Before any human trials can begin, the system must pass rigorous regulatory and ethical review. Key challenges include:

• Preventing infection

• Ensuring stable blood flow through the umbilical vessels

• Monitoring brain development and pain perception

• Defining clear legal and ethical boundaries
  

In the US, any clinical trial would require approval from the Food and Drug Administration. Similar regulatory scrutiny would apply in the UK, where the Human Fertilisation and Embryology Authority and NHS ethics bodies would play a role if the technology were ever proposed for use.

Ethical debate

The prospect of artificial wombs has sparked debate among ethicists, clinicians and disability advocates. Supporters argue that EXTEND could dramatically reduce deaths and severe disabilities associated with extreme prematurity. Critics caution that the technology could blur moral and legal definitions of birth and viability, with implications for abortion law and neonatal decision-making.

Researchers involved in the project say they are mindful of these concerns and stress that the goal is improving outcomes for premature babies, not redefining reproduction.

Looking ahead

While EXTEND remains experimental, experts see it as one of the most significant advances in neonatal medicine in decades. If human trials eventually prove successful, the technology could reshape how doctors care for the most vulnerable premature infants.

For now, EXTEND stands as a powerful example of how bioengineering and medicine are converging to push the boundaries of what is possible — offering hope, but also raising profound questions about the future of birth and early life.