Yes, you can donate your fertilized egg to another couple or to research. It is something that you need to decide when completing the paperwork. Typically, it is on there with What do you want to do with the frozen embryos if one or both partners dies or if there is a divorce.
I know at my clinic, they do allow you to donate eggs and sperm, but I'm not sure about the fertilized egg. Also, the husband and wife have to sign consents and it has to be witnessed in order to do so. I don't know if this has helped or not, but that's all I know. Good Luck!!