Researchers at Cambridge University have grown embryos in laboratory for 13 days, twice the length of time previously possible.

The study has been published on Wednesday, May 4, in journals Nature and Nature Cell Biology. According to Belfast Telegraph this breakthrough could "revolutionize" medicine. However, the lab experiment on human embryos also raises some ethical questions about when life begins.

Scientists were first able to fertilize an embryo in a test tube in 1969. Since then they have never managed to keep one for more than seven days, the point at which the fetus implants in the womb.

Now, researchers at Cambridge University have been able for the first time to grow embryos for 13 days. They only stopped the experiment to avoid breaking the 14 days current legal limit.

Currently up to 70 percent of IVF embryos do not successfully implant. The new research could help improve their failure rate and lead to better understanding of miscarriages.

Better understanding of early embryonic development might also make possible applications in the field of regenerative medicine using steam cells. Doctors believe that these special cells that can turn into any different kind of cell could one day be used to treat heart disease, Alzheimer's and many other medical conditions.

The new breakthrough led to calls for the government to extend the legal limit of 14 days. However, such a measure would be greatly controversial. The limit was chosen in 1980s and is linked to biological changes. After this point, twins do not develop and "individuality" is assigned.

One of the lead researchers, Professor Magdalena Zernicka-Goetz, explained the benefits of observing a human embryo up to 13 days. She told BBC that this it is a great scientific and medical breakthrough. For the first time, scientists can now study human development at the time of implantation, which is a very critical moment, the most mysterious and enigmatic stage of human development.