A system that supports extremely premature lambs in an external artificial womb is demonstrated in Nature Communications. The lambs were supported for four weeks, which is the longest time an extra-uterine device has been shown to maintain stable animal function.
Although the survival of premature human fetuses from 23 weeks of age has been improved by good neonatal intensive care, extreme prematurity is still a leading cause of neonatal mortality and morbidity. However, attempts to design an extracorporeal (out of the body) system that can extend gestation in very premature neonates have not been successful.
Alan Flake and colleagues have developed a closed fluid artificial environment comprising of a polyethylene film bag that incorporates an oxygen circuit via an umbilical cord interface, which mimics the intra-uterine environment. They test the system with extremely premature lambs (biological equivalent of the 23-24 week gestation premature human infant). The authors show that with this extra-uterine system, the lambs have stable blood gas/fetal circulation over the four week study period, and also showed normal development, which included lung maturation and brain growth. Further data on development of the lambs after this incubation period are not available. Therefore, this study lacks data on the effect of such incubation longer term.
This study achieves prolonged survival of the fetuses compared with some previous technologies, which only allowed an animal to survive for a few days. More importantly, these animals maintain normal fetal physiology, which has never before been achieved outside of the womb. A number of issues need to be resolved before application of this system can be considered in humans. For example, the human premature infant is much smaller than the lamb and a specific device for the human would need to be developed, the connection of the device to a human neonate via the umbilical cord may not be possible; the ideal “amniotic” fluid to give to a human fetus would need to be developed and there is no clear outcome on long-term health after such incubation.