Surrogacy happens when mother is having some problem in her body. It can be anything it's not compulsory has to be uterus. Some ppl go for surrogacy if mother is having some disease like heart problem or anything.
In surrogacy. Egg will be mishti's n sperm will be of abir. Dey will go for IVF (in vitro fertilization) just fertilize in a plate dan just implant in some one else uterus.
Egg donation is something else n sperm donation is something else. Most of d ppl r confusing it .