Eggs donated by young, fertile women are needed to overcome various fertility issues. Eggs are the rate-limiting step in reproduction, and any situation that reduces either egg numbers or quality limits the ability to enhance a woman's fertility. The most common issues are natural aging; premature ovarian failure; chemotherapy, or surgical removal of an ovary. Less commonly, a woman may choose not to use her own oocytes to prevent passing a genetic disorder on to her child. Occasionally, same-sex male partners achieve parenthood through the combined use of egg donation and a gestational carrier.