Almost one in three births in 2000 were to single mothers compared to 15.5% in 1991.
The Economic and Social Research Institute (ESRI) Perinatal Statistics report gives an overview on pregnancies between 1991 and 2000.
There was a huge increase in the number of Irish women who had Caesarean sections in that period up 81.5%.
One-in-five births (21%) in 2000 were by Caesarean, compared to one in ten (11.9%) at the beginning of the 1990s.
The average age of mothers who gave birth in 2000 was 30. Most of these mothers had one other baby beforehand.
There was a 3.3% drop in the number of births here in the decade leading up to the millennium down to 55,166 in 2000.
The Crisis Pregnancy Agency said the increase in the number of births to single mothers was in line with trends in other developed nations.
"Not all these births are crisis pregnancies either our experience is that while a high proportion of these mothers are not married, they are in relationships, spokeswoman Caroline Spillane said.
Professor John Bonnar, of the Institute of Obstetrics and Gynaecology, said concerns over the safety of the mother was the main reason for the rise in Caesareans.
"Improved technology allows us to monitor the foetus better and now all breach births are done by Caesarean section," he said.