Scientists have for the first time grown human embryos in the lab for nearly two weeks, a breakthrough that may answer basic questions about human development and help understand early pregnancy loss.
The study shows molecular and cellular processes in human development that occur up to day 14 after fertilisation.
The breakthrough system is the first in which the process of implantation has successfully been replicated outside the uterus, researchers said.
This novel technique vastly expands the ability to answer basic questions about our own development, as well as to understand early pregnancy loss, they said.
Implantation is a crucial step in human development. Occurring shortly after fertilisation, implantation is the process by which the small, hollow ball of cells called a blastocyst attaches to the uterus, allowing an embryo to begin to take shape.
"This portion of human development was a complete black box," said Ali Brivanlou, from The Rockefeller University in US.
The researchers surrounded the blastocyst with just the right chemical environment and provided a suitable scaffolding for it to attach to.
Previous research established a similar method using mouse blastocysts, after multiple attempts to define the right combination of factors.
This prompted researchers to adapt the technique and create an attachment culture for human embryos.
"Through this international and multidisciplinary collaboration combining mouse embryology, human embryology, and physics, we were able to create a system that properly recapitulates what happens during human implantation," said Alessia Deglincerti, from The Rockefeller University.
One known difference between mouse and human development is the shape the blastocyst is in as implantation occurs - it is oblong in mice but shaped like a disk in humans.
"We actually reproduced the disk," said Deglincerti.
Once the system was in place, the researchers determined that the embryos displayed the landmarks characteristic of normal development, including the timing of key events that occur in early embryonic development up to 12 days after fertilisation.
In the near future, the ability to study implantation in culture is likely to shed light on why some early miscarriages occur and why in vitro fertilisation has a high failure rate.
Over the longer term, the work could advance the treatment of a variety of diseases with human embryonic stem cells.
The method opens the door to a wide variety of studies, never before possible, on the molecular events that occur during the very earliest stages of human development.
In accordance with internationally recognised bioethical guidelines, the group's experiments were concluded on day 14 post-fertilisation, well before even the earliest signs of nervous system development are observed.
The study was published in the journal Nature.
