An Oireachtas Committee has heard between 2-5% of children are in a situation where the man they believe to be their father is not their father due to extra-marital affairs.

President of the Irish Fertility Society Dr John Waterstone made the comments at the Health Committee this morning during pre-legislative scrutiny of the forthcoming Assisted Human Reproduction Bill 2017.

Fianna Fáil’s Billy Kelleher stated that "An issue that is raised sometimes, primarily from people who are opposed to IVF and human assisted reproduction, is the whole issue of consanguinity and potential sexual relationships with brothers or half-brothers or sisters and all that flows from that due to the anonymous nature.

Mr Kelleher asked Dr Waterstone to "elaborate on whether that is just something that is being raised to a level that is unnecessary in terms of the debate around this issue, or is it something that we should be conscious of?"

Dr Waterstone responded that "the possibility that a half-brother and half-sister could unwittingly have babies together because they were both the product of the same donor ... is a theoretical possibility.

"But I would like to point out the elephant in the room - in this case it's misattributed paternity.

"There are a lot of people out there who conceive quite naturally without assisted reproduction at all and whose daddies aren't the men they think they are."

"Even conservative estimates say that possibly between 2-5% of children are in this situation where, because of extra-marital affairs, their father isn't the man that they believe to be the case."

He added: "Already in society there is the possibility of unwitting consanguinity. So it isn't just assisted reproduction that can bring about the possibility.

"There is a far more common situation of unwitting consanguinity for babies that are naturally conceived."