It is feared construction of the new National Maternity Hospital will have a negative impact on patients.

The facility is to be moved to the campus of St Vincent's University Hospital, with the move set to be completed by 2020.

However management of St Vincent's has written to the Health Minister Leo Varadkar to say it wants to be reassured existing patient care there and future plans to develop are not affected.

They have outlined fears over the impact that four years of construction will have on its patients.

The letter is understood to have been written towards the end of June - but has only become public knowledge overnight.

Sinn Féin's Health spokesperson - Caoimhghín Ó Caoláin - thinks that other outstanding issues between St Vincent's and the HSE should not be allowed to block the development of the new maternity hospital:

Last month it was revealed that the Department of Health wants to relocate the three Dublin maternity hospitals following a review of services.

Alongside the National Maternity Hospital's move, the Coombe is set to move to St James' - to join the new Childrens' Hospital - while the Rotunda would move to Connolly Hospital in Blanchardstown.

In 2013, there were 20,000 babies born in the three Dublin maternity hospitals - all of which have complained of chronic lack of space.

The announcement followed a review conduced by the Department of Health.

It is understood the plan is to build three new 21st century hospitals.

The total cost for the three moves will be in the region of €450 million (€150 million per hospital), and it is hoped it will be done under the Public Private Partnership model.