Many couples who go for IVF treatments and have a baby (or two) on their first try do give the extra embryos for adoption. The adoptive mother carries the baby to term.
Because of the cost of each treatment, and the likelihood of failure, they usually retrieve as many as 8 eggs at a time. But they don't implant all of those at once. Multiple births can be a problem. So, a couple who has several children and unused embryos has a choice - let another infertile couple have them; discard them, freeze them "in case"; let them be used for research.
Thanks. I knew treatment often meant multiple embryos, I just never heard of adopting them.
It sounds like a good deal all around - everybody gets a baby!