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).
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.
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).