Women are born with a limited number of oocytes (eggs). Eventually the ovary of every woman runs out of oocytes, this is menopause. It usually happens around age 50. Sometimes it can occur earlier at 45 years , 40 or even 30 years of age (premature menopause). In these cases,in order to achieve a pregnancy, oocytes can be obtained from a donor, fertilized in the lab and introduced to the uterus of the recipient, who then carries the baby to term.
It can also be used, in cases where a woman has a hereditary disease that she does not want to pass on to her offspring.