You should bear in mind that the surrogate has the legal right to keep the child, even if it is not genetically related to her.
Surrogacy arrangements are not legally enforceable, even if a contract has been signed and the expenses of the surrogate have been paid.
The surrogate will be the legal mother of the child unless or until parenthood is transferred to the intended mother through a parental order or adoption after the birth of the child. This is because, in law, the woman who gives birth is always treated as the mother.