A quarter of all babies delivered during Ireland's baby boom were from women born outside the country.
Figures show Ireland had the highest birth rate in Europe in 2009 and almost 24% of births were to the country's new Irish. The figure was 17% four years earlier.
Caesarean sections also jumped by a quarter over the past decade, accounting for over 26% of deliveries in 2009.
Elsewhere, researchers found expectant mothers were also 20% less likely to suffer perinatal mortality - the death of a newborn baby or a foetus just before birth - than nine years earlier. The mortality rate was 6.9 per 1,000 live births and stillbirths in 2009, down from 8.9 per 1,000 live births and stillbirths in 2000.
Professor Michael Turner, director of the HSE Obstetrics and Gynaecology programme, said the report shows the perinatal mortality rate in Ireland has improved in the first decade of the 21st century. "There has been a significant decline in both the number of stillbirths and neonatal deaths which is a tribute to all the staff in the different disciplines working in the maternity hospitals," he said
The Economic and Social Research Institute (ERSI) perinatal statistics revealed 76,021 births were reported in 2009, up from 55,186 in 2000. It included 1,186 sets of twins, 13 sets of triplets and one set of quadruplets.
Some 42% were first time mums and almost a third of babies were delivered to single mothers.
Of the non-Irish mothers, 10% were from Accession states, including Latvia, Lithuania and Poland - 4% from Asia and 3.4% from Africa.
"A continuing increase in the caesarean section rate, together with an increase in the number of multiple births, is indicative of increasing complexity," Professor Turner added. "Serious challenges will therefore arise as we aim to ensure a successful outcome of pregnancy for both the mother and her offspring in the face of the decreasing healthcare budget."
The data was compiled from 20 maternity hospitals and 17 independent midwives nationwide.