LONDON • Scientists have for the first time grown human embryos outside of the mother for almost two full weeks into development, giving unique insight into what they say is the most mysterious stage of early human life.

As well as advancing human biology expertise, the knowledge gained from studying these developments should help to improve in-vitro fertilisation treatments and further progress in the field of regenerative medicine, the researchers said.

Scientists had previously only been able to study human embryos as a culture in a lab dish until the seventh day of development when they had to implant them into the mother's uterus.

But using a culture method previously tested to grow mouse embryos outside of a mother, the teams were able to conduct almost hour- by-hour observations of human embryo development up to day 13.

Till this day, a so-called "14-day rule" - which says that human embryos cannot be cultured in the lab for more than two weeks - has never been seriously challenged because no one had succeeded in keeping them alive that long. In this case, the scientists destroyed the embryos to avoid breaching that limit.

"This new technique provides us with a unique opportunity to get a deeper understanding of our own development during these crucial stages and helps us understand what happens, for example, during miscarriage," said Professor Magdalena Zernicka-Goetz of Cambridge University who co-led the work.

The breakthrough is also likely to provide a boost to research on the use of embryonic stem cells to treat certain diseases.

The work, covered in two studies published on Wednesday in Nature and Nature Cell Biology, showed how the cells that will eventually form the human body self-organise into the basic structure of a post-implantation human embryo.

REUTERS, AGENCE FRANCE-PRESSE