Federally funded scientists can also derive stem cells, after informed consent, from aborted fetuses, but this practice is not without controversy.

CNN: NIH publishes draft guidelines for stem cell research

Dr Frisen reckons that they may offer several advantages over human embryonic stem cells which, although easier to manipulate, are a controversial source of new tissue because they are still mainly obtained from aborted fetuses.

ECONOMIST: Stem cells

Supporters of ongoing stem cell research -- which is controversial enough on its own because some existing stem cell lines were created from cells extracted from aborted fetuses -- say the field of study holds the promise of reversing or even curing many diseases.

CNN: Democrat blocks Senate debate of cloning ban

The fetuses that are spontaneously aborted are often abnormally large.

ECONOMIST: Cloning around

The most important consideration in the abortion debate was whether fetuses gestated for 22 or 23 weeks, a tiny number of which are currently aborted, have a better chance of surviving if they are born than they did in 1990, when the existing rule was set.

ECONOMIST: Bagehot