is 14 days. But in light of advancements that may  

now make it possible to culture embryos beyond  those 14 days, scientists and ethicists are discussing:  

should growing human embryos in a  lab beyond this point be allowed?

Okay, hold up. What do we mean when we  talk about lab-grown embryos? Typically,  

these are fertilized embryos that have been donated to scientific  research by in vitro fertilization clinics because  

the embryo is no longer viable for an IVF treatment.  These embryos are different from embryoids.

Embryoids are structures that resemble an early  human embryo but they lack some of the cell types and  

structure to develop into something fully viable.  These are often created in a lab from embryonic  

stem cells, and they can be a useful tool for  studying lots of aspects of human development.

One recent groundbreaking method uses another kind  of stem cell. Scientists take skin cells and hit  

rewind: they reverse them into pluripotent stem  cells, or cells that can essentially develop into  

any tissue type.  

And by exposing them to the right environment,   those cells can be coaxed

into forming a structure that's really similar to

the earliest stage of a human embryo, called  a blastocyst. But because these didn't develop  

from an actual embryo, they are not quite the same as  a real blastocyst, they are called blastoids instead.

The existing 14-day limit on lab-mediated human  embryo or embryoid development was suggested after the first  

IVF babies were born in the 1970s. The media  started to refer to these individuals as 'test  

tube babies', and the scientific community wanted  to make it very clear that embryos were not being  

developed into fully viable fetuses in a test  tube. Instead, IVF is when an egg is fertilized  

with sperm in a petri dish, and those fertilized  eggs usually grow for 2 to 5 days in a lab

before being transferred to the patient's  uterus—and that's technically a lab-grown embryo.

Now, growing an embryo into a fully fledged baby  in a lab, something called ectogenesis, is still  

totally in the realm of science fiction. But after  the development of IVF, there was growing concern  

that maybe developing embryos were being experimented on  or thrown away past certain points in development.

And as the debate rages worldwide  about when life begins, this is and was

understandably a very thorny issue. So a U.S. regulating body proposed  

the 14-day rule just as a guideline, and that limit  actually became a law in at least a dozen countries.

Why 14 days in particular?  

That's the point at which an embryo develops  something called the primitive streak, which  

is the beginning of the body differentiating into  its separate building blocks. It's also the point  

at which becoming a twin is no longer possible,  so that's where 'individuality' is assigned.

And until recently we didn't even know how  to keep human embryos or something similar  

alive in the lab longer than nine days,  so this wasn't really that pressing of a question.   

But 2016 was the year that a couple  research teams got all the way to 13 days.

And ever since, the scientific community has been  grappling with how to deal with these advances  

in the face of the limit... or if the  limit should be changed altogether.  

Because of the advancements in our ability to  grow these structures in the lab for longer,  

and the exciting developments in blastoid and  embryoid research, there's now the possibility  

of investigating parts of human development  we've never had access to before. This could  

help us understand why some miscarriages  happen, or how some birth defects develop.

We'd be able to see the effects of all kinds of  chemicals and medications on embryonic development  

and maybe make IVF safer and more effective. 

But would a new time limit only mean good things?

What about the possibility of  genetically modifying human embryos in  

new ways—we're gonna need to think about  that one REAL hard. And at what point can  

scientists ethically say that a blastocyst  is no longer a clump of cells and is instead,  

a fetus? And what do we do with  a lab-grown embryo at that point?

We're going to need plans in place for all of this.

Ever since the 14-day rule was  first proposed in the 1970s,  

experts in this field from scientists to  philosophers have known that we would one day  

have to revisit this because of scientific  advancements. And that day has arrived.

The International Society for  Stem Cell Research, or the ISSCR,  

released its updated guidelines for  culturing human embryos and embryoids.  

They are calling for a public conversation  with ethicists, scientists, and regulators

about the social and ethical issues associated  with going past 14 days. How this may translate  

into legal changes in some countries remains to be seen, and lots of questions we talked about before remain unanswered.

What do you think about extending the  14 day rule? If you're interested in these public

conversations make sure you check out the link in our description for more details.

Make sure to subscribe to Seeker for all of your boundary-pushing biomedical news.

And if you have another stem cell  development you want us to cover on the channel,  

let us know. As always, thanks so much  for watching and I'll see ya next time.