A surrogate is a woman who carries the fertilized egg to term in her uterus on behalf of the intended mother. There are two kinds of surrogacy: classic and gestational. A classic surrogate is inseminated with sperm from the child's father. Her own egg is fertilized, and she carries the baby to term on behalf of the patient.

In gestational surrogacy, the baby may be conceived entirely by the intended parents-the biological mother's egg is fertilized with the biological father's sperm-or by one or more donors. The embryo is then placed in the surrogate's uterus and carried to term.

Gestational surrogates may be relatives or friends, or they may not have met the couple before. The best candidates are highly committed women under 40 with proven fertility and at least one healthy child. Potential surrogates will undergo medical and psychological testing and are advised to seek legal advice before the process.

Once a surrogate is selected, she will undergo a "mock cycle," during which she will be given most or all of the fertility hormones administered during the IVF process. This allows the physicians to make sure that there are no problems with the uterine lining. After the cycle is complete there will be a "mock transfer" where the cervix angle and uterine cavity length are measured in preparation for the actual transfer.

The surrogate and female partner or egg donor are then given birth control pills to synchronize their menstrual cycles. Lupron, estrogen and other medications are then given to stimulate fertility in the donor and prepare the uterine lining in the surrogate. The eggs are retrieved, fertilized with the male partner or donor's sperm and then one or more are transferred to the surrogate, who carries the fetus to term if implantation is successful and pregnancy results. Any unused embryos may be frozen.

For more information on gestational surrogacy, click here.