Certain conditions necessitate use of donor gametes i.e donor eggs/ sperm. Egg donation may be needed for cases with poor ovarian reserve, poor egg quality, maternal genetic conditions that may be passed on to offspring , premature ovarian failure. 

Sperm donation can be used for cases where male partner is azoospermic, no sperms in ejaculate, poor sperm quality , certain genetic conditions that can be passed on to offspring.