There were more than 61,000 babies born in Ireland last year, a slight decrease on the previous year.
There were 61,016 births in 2018 compared to 62,053 in 2017.
The CSO figures show the average age of Irish mothers is 33.
Limerick has the highest percentage of births outside marriage at 54%, the lowest is in Dun Laoighre in Dublin with 23.8%.
A total of 980 teenagers had babies in 2018 – 22 of them were under 16.
The figures show Dublin city has the highest number of births registered (7,041), followed by Cork (5,541).
Leitrim has the lowest number 399 births, accounting for 0.7% of total live births in the country.
There were 187 infant deaths registered in 2018 giving an infant mortality rate of 3.1 per 1,000 live births.
There were 31,116 deaths were registered last year resulting in a natural increase in the population of 29,000 people.
Of the 31,116, 15,967 were male while 15,149 were female.
That total is 2.1% higher than in 2017 when 30,484 deaths were registered.
Diseases of the circulatory system accounted for 8,938 deaths while there were 9,198 deaths from malignant neoplasms.
Deaths from chronic lower respiratory disease numbered 1,743, pneumonia accounted for 1,084 deaths.
The CSO says that the number of marriages registered in 2018 was 21,053.
664 were same-sex marriages.