[pygy_]

AFAIK, they use the embryos left after a successful IVF (if the parents agree).

The sucess rate of an IVF is relatively low, and the procedure to extract the ova is complex, inconvenient and not risk-free.

Ovaries are overstimulated to produce more than one egg. They are all collected and fertilized, but, usually, only two or three are implanted at a time, to balance the low success rate and the non-null chance of multiple pregnancy (that's how octuplets are made :\).

If a successfull pregnancy occurs before running out of embryos, the mother/couple may donate the remaining embryos for research (that's how it works in Belgium, at least).

[Serow225]

Current practice from the doctors I've talked to in North America is to encourage people to implant one egg per attempt, with two eggs being allowed if the couple insists.

[riggins]

I really struggle to understand people who view prohibiting the use of embryos that would be thrown out otherwise as supporting 'life'.