The High Court has been told there is no provision to record genetic parents of children born to surrogate mothers on birth certificates.
The country's Chief Registrar was giving evidence in a landmark case on surrogate births.
The case is being taken by the parents of children born to a surrogate mother who want the genetic mother's name recorded on the birth certificate.
Chief Registrar Kieran Feely told the court he became aware of the case after a request was made at a register office.
He informed the registrar that only the woman who gave birth to the children could be recorded on the birth certificate as the mother.
Mr Feely said it was the first or second case involving surrogacy to come before him.
Two cases arose almost simultaneously. He said he was aware from the time of his appointment that that this was the way cases of surrogacy were dealt with.
Mr Feely said he was not aware of the genetic inheritance of the children until he got a letter in 2010 from a solicitor asking to have the register of births corrected to include the genetic mother of the children.
The couple had asserted that the name on the register of the woman who gave birth as the mother to the children was not correct.
Mr Feely carried out an inquiry and was supplied with DNA evidence and a letter from an IVF clinic outlining what had transpired.
He said "the net effect was to tell me the genetic mother was different from the mother who had given birth".
Mr Feely said he came to a decision that he did not have the power to make the correction and informed the couple's solicitor by letter in 2011.
"The legal mother is the mother who gave birth to the children so there was no legal basis for me to make the correction," he said.
Mr Feely said he had independent evidence from the hospital about the woman who gave birth to the children and he applied the principle of "Mater certa semper est" - motherhood is always certain.
He said the benefits of the current system were the simplicity and certainty around it.
If it were the case that genetics had to be inquired into for the registration of births it would create an enormous amount of uncertainty and possibly cost. He said he could not see how it could be done in practice.
It was suggested to him that the system could work the way it works for paternity in that there is a presumption of paternity. Mr Feely replied:"Motherhood is a fact, paternity is a rebuttable presumption."
The case continues before Mr Justice Abott. A number of reporters were allowed into the case for the first time today. Reporting restrictions have been applied in order to protect the family whose evidence has been heard in private.