A technique has been developed that for the first time allows scientists to study the development of an embryo beyond the stage when it would normally “implant” in the womb.
The research is controversial because it pushes against the UK legal limit for keeping an embryo growing in a laboratory, which is 14 days after fertilisation.
Two international teams of scientists, including British researchers, were able to maintain living embryos under lab conditions for up to day 13 of development, opening new doors for investigating causes of infertility.
Until now it has only been possible to study early-stage “blastocysts” - tiny balls of cells - during the few days before an embryo attaches itself to the inner wall of the womb.
Implantation has to take place on the seventh day of development if an embryo is to survive and develop further.
Failure of an embryo to implant is a major cause of early pregnancy loss, but the cellular and molecular changes that cause this to happen are still not well understood.
Prof Magdalena Zernicka-Goetz, from Cambridge University, who led the British scientists and was a participant in two parallel studies published in the journals Nature and Nature Cell Biology, said: "Implantation is a milestone in human development as it is from this stage onwards that the embryo really begins to take shape and the overall body plan is decided.
“It is also the stage of pregnancy at which many developmental defects can become acquired.
“But until now, it has been impossible to study this in human embryos. This new technique provides us with a unique opportunity to get a deeper understanding of our own development during these crucial stages and help us understand what happens, for example, during miscarriage.”
The advance increases pressure to relax the law on conducting experiments on human embryos, enshrined in the 1990 Human Fertilisation and Embryology Act.
Independent policy advisers the Nuffield Council on Bioethics now plans to review its position on the law.
Chairman Johnathon Montgomery said: “Later this year, the council intends to bring together invited participants with a range of perspectives on embryo research in order to evaluate whether, after 25 years, there may be persuasive reasons to review this legal limit, or whether the reasons for its introduction remain sound.”
The scientists used an improved culture medium and provided an efficient way for the human embryo to attach itself to a laboratory Petri dish before continuing its development.
They watched embryos re-organise themselves and start to differentiate into different cell types, forming a structure containing a cavity vital to future development.
Prof Zernica-Goetz said: “Without this cavity, it would be impossible for the embryo to develop further as it is the basis for its future development. It is also a mechanism that we can study using human embryonic stem cells.
“This process is similar to what we have recently observed in mouse embryos, despite the significant differences in the structure of post-implantation embryos in these different mammalian species. This suggests it may be a fundamental process conserved across many species.”
‘Complex process’
Colleague Dr Marta Shahbazi, also from Cambridge University, said: “Embryo development is an extremely complex process and while our system may not be able to fully reproduce every aspect of this process, it has allowed us to reveal a remarkable self-organising capacity of human blastocysts that was previously unknown.”
Dr Simon Fishel, another member of the British research team and founder and president of leading IVF clinic chain CARE Fertility Group, said the work was about “much more” than understanding the biology of embryo development.
He said: “Knowledge of these processes could help improve the chances of success of IVF, of which only around one in four attempts are successful.”
Leading fertility expert Allan Pacey, professor of Andrology at the University of Sheffield, described the work as “very elegant” and said it opened up “exciting” potential for future research.
“There will no doubt be people who will be opposed to this kind of research and may disagree fundamentally with the idea that legitimate and ethical research on human embryos can take place for up to 14 days in the laboratory.
“Whilst I respect the strength of their views and their conviction, this is a framework which was agreed over 30 years ago and I see no reason to change or revisit that decision.
“It will not open the door to couples being able to grow babies in the laboratory; this is not the dawn of a Brave New World scenario. But it does open up exciting opportunities to understand the nature of human disease and disability and for that reason the scientists involved should be congratulated.”
PA