A report by the Health Information and Quality Authority on the National Maternity Hospital at Holles Street in Dublin has found overcrowding and very poor hygiene.
HIQA inspected the hospital in October last year.
It found there were too few delivery rooms and in the neonatal intensive care unit 46 babies were accommodated in a unit designed for 36.
HIQA said this increased the risk of infection.
It also found a fire exit partially obstructed by a baby cot.
Other examples of poor hygiene included unsafe injection practices, poor management of clinical waste and no local hand hygiene audits.
It also found that cleaning resources remain relatively unchanged while demand had increased.
Environmental hygiene was very poor in the delivery ward.
A follow-up inspection six weeks later found some of the cleaning issues had been addressed but HIQA was told the hospital could not address the overcrowding because of space restrictions and current demand levels.
In a statement, the hospital said: “At the heart of this story is an activity level that far exceeds the capacity of the building.
"It is for this reason that for the past 20 years the hospital has sought relocation to a modern facility that is fit for purpose."
The National Maternity Hospital is due to move to new facilities in 2018.