The Supreme Court has been told the genetic parents of twins born to a surrogate believe it is unreasonable for the State to argue they should adopt the children rather than be recognised as their legal parents.
The couple see the twins as their children.
They cannot understand why they should have to go down the long, drawn-out and intrusive route of adoption, their lawyers told the seven-judge court.
Senior Counsel Gerry Durcan said the surrogate in this case was the sister of the genetic mother, and adoption is easier if it involves a relative.
However, he said the court should bear in mind its decision on this case will have implications for all those involved in surrogacy arrangements.
In this case, adoption might solve some of the problems raised but it would not resolve them all and, in other cases involving surrogacy arrangements, adoption would not be an option at all, he said.
This couple had found themselves in a position where they did not have "the luxury of legislation", counsel said.
Families cannot wait while the legislature gets around to catching up, in a large way, with the developments in assisted reproduction, he added.
The couple had made a decision essentially "to have a new life" and the law allowed them to do what they did.
Legislation has to be fashioned to respect the constitutional rights of all involved, including the children, and legislature has a lot of discretion in relation to how it handles such situations, he added.
The court was also told that legislation dealing with assisted reproduction issues must protect the rights of all involved, especially children.
Senior Counsel Nuala Butler, for the Equality Authority and the Irish Human Rights Commission, said scientific developments in this area are rapidly changing and, while there is no consensus among EU states concerning how surrogacy should be dealt with under law, there may be in ten to 20 years time, she said.
She could not see how the State could argue that the High Court decision in favour of the genetic parents being registered as the legal parents of the children in some way restricted the State's freedom to legislate in this area.
Motherhood is not just based on genetic links or on giving birth but is something much broader, including pregnancy, birth, rearing of children and social and family links, she said.
The lawyers were making arguments in the State's appeal against a High Court decision that the genetic parents are entitled to be registered as the twins legal parents on their birth certificates.
The twins were born to a surrogate, a sister of the genetic mother after she was implanted with genetic material from the couple.
Because the genetic mother was unable due to a disability to carry a child herself her sister agreed to do so as a gesture of love.
In its appeal, the State contends the woman who gives birth to a child is the legal mother of that child.
It also argues that proposed new laws will address the position of the genetic parents and that the court should not uphold the High Court decision because that will have implications for, among others, women who have had children using donated eggs.
The appeal is continuing.