One third of all births are outside marriage, according to new figures compiled by the Economic and Social Research Institute (ESRI).
The figures, from 2010, show that 65.6pc of all births in that year were to married women, as compared to 32.8 for unmarried women.
There were 75,245 births in total. The figures, published on Monday, showed that the number of births outside marriage had remained relatively consistent since 2006.
Overall, the figures showed that Irish women are waiting later to have children.
The average age of mothers has increased from 30.3 years in 2001 to 31.5 years in 2010
According to the figures, 28pc of mothers were aged 35 years or older, up from 22pc in 2001, while 16pc of first births were to women aged 35 years or older compared to 10pc in 2001.
The figures also suggest that fewer women are giving birth in their teens; 3pc of mothers giving birth were aged 19 years or younger, compared to 5pc in 2001.
The average age for first time mothers was 29.4, and 42pc of those who had children were giving birth for the first time. The average age for single mothers was 28 years old.
The figures also showed a rise in the number of children born to non-nationals. According to the report, 25pc of births in 2010 were to mothers born outside Ireland compared to 18pc in 2006.
After births to mothers from Ireland the next highest proportion of total births were to mothers from the EU15 to EU27 at 11.3 per cent, followed by mothers from Asia at 3.9 per cent.
Over the period 2006 to 2010 the proportion of births to Irish mothers fell from 81.6 per cent to 75.5 per cent.
The proportion of total births to mothers from Africa decreased slightly from 4.0 per cent in 2006 to 3.0 per cent in 2010.
The average age of all mothers giving birth was 31.5 years and the average age of mothers from Ireland was slightly higher at 31.9 years.
Mothers giving birth from the EU15 to EU27 were on average younger at 28.6 years, whilst mothers from Australia recorded the highest average maternal age at 33.6 years.