Surrogacy is defined as the condition where a couple, who is unable to have children - due to fertility issues, age, etc. hire a womb or resort to another woman to carry the child for them. Surrogacy has been mentioned in the bible when Abraham and his wife Sarah were unable to conceive. Ancient India too has witnessed many queens and kings resorting to surrogacy for bearing the kin to the throne. The woman whose womb is colloquially hired or who eventually gives birth to the baby is known as the surrogate mother.
Contemporary surrogacy took form in the U.S when the first legal or official agreement had been formed for the same around the 70’s. The lawyer who had brokered this agreement then founded an Infertility Centre for surrogacy birth. It was during this period that the Louise Joy Brown, the first "test tube" baby gave way to the idea of gestational surrogacy.
So, basically in this kind of surrogacy, the sperm and egg are implanted into the surrogate mother's uterus. This is a form of surrogacy that most people prefer now, consider the biological compatibility. The other common process is the conventional form of pregnancy. Here the sperm is artificially inserted into the womb of the surrogate mother. But in this case, the genes of the surrogate mother are transferred to the child as it is her eggs that are fertilised with the fathers. Hence a genetic link is established and the surrogate becomes the biological mother of the child.
On the whole, legal contracts are made for considering the process of surrogacy. With mothers changing their mind and psychological stress, a contract perhaps is a safer legal way to ensure that you go home with a healthy baby.