278 newborn babies may have been incorrectly blood-grouped at birth following revelations that potentially mislabelled test kits were used in five hospitals.
Sligo Regional Hospital along with Cavan General, The Rotunda, Limerick and Galway hospitals are at the centre of the alert issued by the HSE.
The blunder first came to light almost two months ago but mothers only learned last week if they had been affected.
The HSE has insisted it is extremely unlikely anyone will have been affected by the error, and it has contacted all relevant parties.
The hospitals involved only started contacting affected mothers last Monday, 12 August.
There was a batch of around 540 mislabelled kits issued.
Info line: 1850 24 1850.