When the female partner is unable to produce the eggs due to various reasons like menopause, premature ovarian failure or age factor,then the infertile couple seeks a woman who would donate her eggs.
These eggs are fertilized and implanted in the womb after which children are born naturally.
The female has to undergo two to three sessions of hormonal therapy before obtaining eggs from the donor.
It is called Hormonal Replacement Technique(HRT). The therapy is used to determine compatibility.
When the male partner has zero sperm or when his sperms are of low-quality, the couple will need some other male who is willing to donate sperm.
They are used to fuse with eggs of the female partner to form an embryo.
That embryo would then be implanted in the womb to produce a healthy child after 9 months.