There is widespread opposition to using such embryos to make babies.

You know that you were born as part of an illegal scientific experiment using embryos stolen from your parents.

"There's a significant weight to the decision to use human embryos," he says.

So stem cell research that uses human embryos has now effectively been cut.

Women in their late 20s through mid 40s average about a 50% birth rate using fresh (not frozen) embryos.

Complicating the president's decision is the fact that some anti-abortion conservatives favor research using human embryos.

She probably figured they wouldn't go after her because she was no longer using embryos.

In fact, women using fresh embryos (not frozen), have a 43.4% chance of getting pregnant in each cycle.

It contains no comprehensive rules on research using embryos and embryonic stem cells.

The legitimacy of research using embryos is one the most complex and sensitive ethical questions which can arise in science.