The woman agreed to act as a surrogate so that her sister, who was unable to carry a child, could have what she had and experience motherhood, the court was told.
However the genetic mother could now face a raft of problems - from being unable to give permission for emergency medical treatment to seeing her children unable to automatically inherit her estate - as she is not legally recognised as the twins' mother.
In a landmark legal case, the genetic parents of the twins are seeking to have their children's birth certificates amended to name the genetic mother rather than the woman who acted as surrogate.
The surrogate mother is supporting her sister's application which is being opposed by the Attorney General.
None of the parties can be identified for legal reasons.
The High Court also heard evidence from an expert in assisted human reproduction.
Dr Mary Wingfield, who gave evidence for the State, said that the failure by the Government to introduce legislation for the area is "very disappointing" and "tragic".
Dr Wingfield, a Consultant Obstetrician Gynaecologist at the National Maternity Hospital, and a director at the Merrion Fertility Clinic, Dublin, said that the lack of regulation in the area has resulted in people taking High Court actions.
The Attorney General and the Office of the Registrar General are opposing the action, on grounds including that the surrogate or gestational mother is in law the mother of the child.
Dr Wingfield said she was a member of the Government-appointed Commission on Assisted Human Reproduction, which made a number of recommendations on issues including that of surrogacy.
The commission published a report in 2005 but none of the recommendations have been made law. The majority agreed that the "commissioning parents" should be presumed to be the parents. She said it was "very disappointing" that Ireland "was no further on" in the area of assisted reproduction.
The case continues.